Editor’s note: This is an updated version of an article published in 2018 and 2019.

Opinion post by Robert Triggs

USB-C is billed as the solution for all our future cable needs, unifying power, and data delivery with display and audio connectivity. Ushering in an age of the one-size-fits-all cable. Despite the USB-C connector supplied as default in modern smartphones, the standard has, unfortunately, failed to live up to its early promises.

Read next: What are the best USB-C headphones?

Even the seemingly most basic function of USB-C — powering devices — continues to be a mess of compatibility issues, conflicting proprietary standards, and a general lack of consumer information to guide purchasing decisions. The data speeds available over USB-C have also become increasingly convoluted. The problem is that the features supported by different USB-C devices aren’t clear, yet the defining principle of the USB-C standard makes consumers think everything should just work.

A good example of USB-C compatibility problems: Charging speed

There is a very common frustration with the USB-C standard in its current form. Moving phones between different chargers, even of the same current and voltage ratings, often won’t produce the same charging speeds. Furthermore, picking a third party USB-C cable to replace the often all too short in-box cable can result in losing fast charging capabilities. As can opting for a third-party USB-C power adapter that supports Qualcomm’s Quick Charge or USB Power Delivery rather than one of the numerous proprietary standards.

We’ve tested this numerous times in the past and found that USB-C phones from popular brands, including Samsung, Huawei, LG, Google, and OnePlus, all slow down their charging speeds once you begin to mix and match cables and chargers.

More about USB-C: How fast charging really works

Even the most recent flagships offer drastic disparities between supported speeds and standards. The OnePlus 8 Pro, for example, fails to Warp Charge at 30W if you deviate from the in-box cable. Not great if you break or lose the provided cable. The Google Pixel 4 outright refuses to charge with Huawei cables, perhaps because they break official USB-C specifications in some way, according to Google. So don’t bank on being able to charge up using your friends USB-C adapter or USB-C connector.

2020 flagships still prefer proprietary chargers over other manufacturers.

The graph below showcases how mixing and matching cables and chargers drastically reduces USB charging speeds compared to the cable and charger provided in the box. The take-away is that charging speeds over USB-C vary widely from handset to handset.

The good news is that USB Power Delivery (PD) is now pretty well supported for fast charging, albeit usually at a slower speed than the in-box charger. When supported, Quick Charge is notably slower. Phones that use USB PD as their default charging tech also perform better when swapping cables and chargers than those that use proprietary standards. See how the Samsung Galaxy S20 compares to the OnePlus 8 Pro, for example.

While this is a step in the right direction, USB Power Delivery is quickly suffering from standard fragmentation too. The introduction of Programmable Power Supply (PPS) in the USB PD 3.0 spec led to great confusion about 45W fast charging with the Samsung Galaxy Note 10 Plus. Now consumers don’t just have to look out for USB Power Delivery, they also need the PPS variant for some devices. Confused?

45W charging with the Note 10 Plus requires USB PD 3.0 PPS, not regular USB PD. Confused?

USB Power Delivery – the broader picture

We’ve continued to explore the discrepancies in charging support for Power Delivery and Quick Charge standards in a wider range of devices too. We’ve compared this to boxed charger speeds and support from generic USB 2.4A ports. You can find the data in the table below. Results highlighted green provide good fast charging support, while yellow indicates an OK implementation, and red a failure to support the standard in question at a decent speed.

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The notable trend over the past couple of generations is that USB Power Delivery support has overtaken Quick Charge 3.0. Although this could be in part due to Quick Charge 4’s compatibility with Power Delivery. USB PD is increasingly supported by laptops and tablets for charging too, making it more likely you can find a single USB-C adapter for all your gadgets.

Support for Quick Charge has wained, but USB Power Delivery now widely supports fast charging.

USB Power Delivery speeds hover around 15W typical, while Quick Charge 3.0 is often below 9W. However, the mixed bag of results highlights the broader issue perfectly. There’s a huge range of speed results here. Smartphones also often hide support for these standards in a spec table and even then there’s no guarantee that consumers know what these standards mean. Even if a phone supports both third-party standards, it may charge significantly slower than when using the boxed charger.

Related: The best USB-C cables you can buy

Ultimately there’s still very little consistency about the charging speed of smartphones and no easy way for consumers to know if, or how well a handset will charge using any given standard. This becomes even less clear when products start using bi-directional charging capabilities, such as charging your phone from your laptop’s USB port.

More than just charging: USB-C speed for data

Charging is still overly complicated then, and it’s the same situation with data transfer speeds. USB-C support 2.x, 3.x, and Thunderbolt speeds for some ports, which is confusing enough. However, cables also have to be specifically rated to meet higher speed requirements.

The introduction of USB 3.2 and its ridiculous Gen 1 and Gen 2 branding threw up another hurdle for those trying to get their head around the increasingly complicated naming scheme. Just days later, the USB 4 announcement drained any remaining comprehension from consumers and developers alike. USB 4 claims to “minimize end-user confusion”, as it mandates a USB-C connector and USB PD support, but it still offers a confusing array of optional features, such as Thunderbolt 3 on just some devices. Even so, it will be a long time before USB 4 devices permeate the market in sufficient numbers to make any difference. Unfortunately, consumers still have to wade through this branding quagmire to figure out what’s supported.

There's no way to tell if a USB-C cable supports high current charging or 4.0 data speeds just by looking at it.

The USB data naming scheme is undoubtedly a mess. This table below will hopefully help to sort out what each specification offers you.

Generation Specification Optional Consumer Branding Dataspeed USB 1.x USB 1.0 Full Speed USB 12 Mbps USB 1.0 Low Speed USB 1.5 Mbps USB 1.1 Full Speed USB 12 Mbps USB 2.x USB 2.0 High-Speed USB 480 Mbps USB 3.x USB 3.0 SuperSpeed USB 5 Gbps USB 3.1 Superspeed USB+ 10 Gbps USB 3.2 USB 3.2 Gen 1 SuperSpeed USB 5Gbps 5 Gbps USB 3.2 Gen 2 SuperSpeed USB 10Gbps 10 Gbps USB 3.2 Gen 2 2x2 SuperSpeed USB 20Gbps 20 Gbps USB 4 USB 4.0 40 Gbps (Thunderbolt 3)

Devices and cables are just as problematic when it comes to supporting “Alternate Modes” and other protocols. These fall under the USB-C specification rather than the port’s data speed specification. These include DisplayPort, MHL, HDMI, Ethernet, and audio functionality provided over the connector, all of which rely on the connected devices and cables to support them. These are not a compulsory part of the port specification, as capabilities and needs clearly vary from device to device. USB 4, for example, introduces DisplayPort 4.1a and PCI Express data support, but you don’t need that on a battery pack.

The problem with this is that certain functionality that a user might expect in a product isn’t necessarily provided. Consumers may assume HDMI or Ethernet are supported over a USB-C port if a laptop is missing the regular ports, but that might not be the case. Even more frustratingly, functionality might only be restricted to specific Type-C ports on the device. You might have 3 ports but only one that offers the functions you want.

USB-C is compatible with lots of features, but not every port supports everything. USB 4 does too little too late to help.

USB-C makes functionality more opaque, not less. It claims to do everything, yet there’s still no guarantee a product will actually work with any of these features. USB 4 may help unify some feature compatibility, but I doubt it will help end confusion while USB-C 3.1 and older ports still exist. The sheer range of legacy devices and remaining optional standards means that USB-C port capabilities remain unknown at a glance. Even when more detailed information is available and ports are correctly marked with the appropriate branding, making heads and tails of the various modes and jargon can be a lot of information for someone to digest when all they want is something that works.

Tested: The Google Pixel series has a strange USB-C transfer problem

Port shortages are a problem

This brings us nicely to the biggest problem with the reversible USB port, at least with smartphones: there’s a lack of them on devices. A single port for audio and power is already proving problematic in the handset space, with consumers reaching for dongles and hubs to fix the issue at their inconvenience. However, this opens up a whole new world of compatibility problems, such as whether your hub or dongle supports the same charging method or standard for bi-directional power, or if data can still pass through to another device.

Trial and error is often the only way to figure out what a USB-C port supports.

It’s a similar situation with a number of the latest laptops on the market. Although this is device-dependent, as some new models sport charging, audio, and other features on multiple USB-C ports. Even so, ditching the power socket for USB-C instantly reduces your peripheral count when powering up the device, which is particularly frustrating considering most laptops only have a couple of available ports to begin with. Users are increasingly forced towards dongles to connect up to legacy ports that are still ubiquitous in other marketplaces.

Part of this is due to the fact that although USB-C has made its way to laptops, it’s still rarer to find on mainstream displays and common accessories. All the new port has done is push some components out of the laptop and onto the other end of the cable. Not exactly a consumer-friendly move, given the prices often charged simply to regain the functionality of older products.

Why the compatibility issues?

Cable compatibility, arguably the most frustrating of USB-C’s problems, stems from legacy support for slower devices and the introduction of higher-speed use cases like video data. USB 2.0 features just four-pin connectors for data and power, while 3.0 cables increases this to eight. So USB-C to A cables, which are commonly used for charging, can come in 2.0, 3.0, and 3.1 varieties, which affects the amount of data and power they can handle. USB Power Delivery is backward compatible and so is the best option for charging up devices using older cable types and speeds, but the prevalence of proprietary standards means consumers rarely really know what they are getting.

Cable quality, rating, and length affect the features available over a USB-C port. Some cables even breach the standard!

Cable quality also comes into play here, as some charging standards will detect how much power a cable can handle and set the appropriate charging speed. In our earlier example, Huawei’s technology requires a 5A rating to charge at full speed (but breaks spec and doesn’t work with the Pixel 4). This is why longer cables from third parties won’t always offer the same speeds as the smaller ones included with your phone.

If that wasn’t complicated enough, the introduction of high-speed data and real-time video transfer has introduced new problems. Very fast signals suffer from attenuation and clock jitter when transferred over long distances, meaning data can get lost along the way. To address this issue cables can also come in passive or active varieties. Active cables include redrivers to restore the signal amplitude and prevent a loss in signal quality over long distances. So long cables used for very high data speeds (such as sending 4K 60fps video or data over Thunderbolt) require active components in them, while basic charging and data transfers can get away with a standard passive cable that’s less than two meters long.

DisplayPort, MHL, HMDI, and Thunderbolt are supported via passive USB Type-C cables at less than two meters if they carry the “trident” SuperSpeed USB logo or less than one meter for SuperSpeed+ labeled cables. Active cables will be required for further distances and you’ll have to look out for the Thunderbolt logo if you want 40Gbps speeds. Passive adapter cables to other USB types won’t support any of these modes.

Feature compatibility issues also involve the port and device in question, which can be configured for a wide selection of charging speeds, legacy standards, and alternate modes. USB-C is a more complex port than its predecessors, requiring substantially more software and hardware input to get things working correctly.

The starting point for USB-C products is the Power Delivery protocol. This isn’t just about charging, it’s also how the port communicates support for extra features like HDMI and DisplayPort by using the connectors additional pins. All of the Alternate Modes use the Power Delivery Structured Vendor Defined Message (VDM) to discover, configure, enter, or exit these modes. The bottom line is that if your device doesn’t support Power Delivery, it won’t support any of these other features either. Unfortunately, Power Delivery circuitry is more complicated and expensive than the barebones circuity, and the complexity scales up with the number of ports.

USB-C audio is basically dead as Bluetooth takes over.

Even so, this doesn’t mean every Power Delivery port or device will support every feature. It’s up to device manufacturers to include the necessary multiplexers and other ICs alongside the Power Delivery components and regular port connections to support Ethernet, display, and other Alternate Modes. The diagram below shows just some of the different component blocks required to scale up the feature set of just a single USB-C port.

The port circuitry only becomes more complicated when products want to route and manage multiple signals, such as video or audio, to multiple USB ports. The signal routing becomes increasingly complex and expensive so manufacturers restrict functionality to only one or two ports.

Even delivering power requires a complicated circuit with USB-C, in order to accommodate for the reversible connector type, the range of power options, and the choice between upward, downward, and bi-directional charging port and data options. To cut down on costs and complexity, not all USB-C ports on a laptop or PC sport everything. USB 4 aims to help by mandating a few features, but that seems unlikely to help if devices mix and match new and old standards to save on costs and complexity.

USB-C will remain a mess

USB-C’s complexity is undoubtedly its undoing. Although the idea of one cable to support everything sounds very useful, the reality has quickly become a convoluted combination of proprietary versus on-spec products, differing cable qualities and capabilities, and opaque feature support. The result is a standard that looks simple to use but quickly leads to consumer frustration as there is no clear indication as to why certain cables and features don’t work across devices.

At the same time, product developers are facing a similarly frustrating situation. Supporting the full range of advanced USB-C features is a complex engineering feat, far more so than previous USB generations. Furthermore, the increasing number of components and connectors is raising development costs and deployment time. While there are now more integrated ICs and USB 4 to ease compatibility, the sheer range of options and features in the latest specification makes implementation expensive and time-consuming.

Not all USB-C ports or cables are equal. Despite efforts to unify, USB 4 can't fix the compatibility problem.

USB 4 is a mixed attempt to unify the USB-C port, and it certainly can’t solve the problem on its own. Better labeling could help consumers identify which cables and products support which features — so far the naming schemes and logos have been rather unfriendly for casual glances. Mandatory cable and port coloring, as was the case with USB 3.0 ports, could help, but it kind of defeats the whole purpose of this one size fits all solution. An even more strictly enforced standard is needed to help consumers get their heads around compatibility will help.

Related: Why are phones still shipping with terrible wired charging speeds?

Unfortunately, the USB-C ecosystem is more, not less convoluted in 2020 than it was when I first looked at this issue back in 2018. The announcement of USB 3.2 and USB 4 makes the standard more complex without giving the end-user clear information about what’s supported. While the growth in USB Power Delivery support is a good sign, the introduction of PPS has already hampered any hopes that the industry might soon coalesce around a single charging standard. The USB spec changes every year, making it impossible for consumers to keep up.

Years later, I still don’t see a clear way out of this confusing mess.

Looking for some more data-based analysis else to dig your teeth into? Check out some of our testing content below:

This table shows which Alternate Mode protocols are supported by which cable types.