In theory, all USB-C cables should be the same: that’s the whole point of having a standard. In practice, there are different versions of the standard. More worryingly, many cables being sold as USB-C don’t fully conform to that standard – and that can be seriously bad news …

Some non-compliant cables simply won’t offer the full data speeds they promise. Others can’t be used for data at all. And yet others can draw too much power, which can not only damage any device you’re charging it with, but could even damage the USB port in your MacBook.

That latter problem is specific to older MacBooks, with a USB-A port. Those were designed with a maximum current draw as part of the spec. USB-C devices can draw significantly more power, so if you use a USB-A port to charge a USB-C device, then a non-compliant cable can draw more power than the port is designed to handle. That can damage both the device you’re charging and your MacBook. A compliant cable has a resistor to limit the current draw.

But the data and speed problems apply equally to MacBooks with USB-C ports. So, how do you ensure you’re buying a cable which is safe, supports data, and offers the full transfer speeds on offer? There are three methods you can use.

The first, and simplest, approach is to stick to reputable brands you can trust to adhere to the standards. Apple is an obvious one, but buying a trustworthy brand doesn’t necessarily mean paying Apple prices for your cables. Amazon Basics are another brand which adhere to the standards, and are significantly cheaper.

Second, look for the SuperSpeed+ (SS+) logo. However, not all cables use the full logo, and may not distinguish between the older SS and newer SS+ labels. Some also use SS and a 10 to indicate 10GBps, instead of SS+, like the one above.

For that reason, it’s best to use the third method: look for the USB generation label, and make sure it’s USB 3.1 Gen 2, which supports 10Gbps (in contrast with USB 3.1 which is limited to 5Gbps). Just to complicate matters, you may also see USB 3.0 and USB 3.1 (with no generation suffix): these are older labels for USB 3.1 Gen 1 and Gen 2. The safest bet is to specifically look for USB 3.1 Gen 2.

Unless you want a cable only for charging purposes, beware of cables labelled ‘charge cable’ as that’s an immediate giveaway that they don’t support data transfer. This includes the charge cables Apple supplies inside product boxes.

There is, though, one last complication: Thunderbolt. This uses the same physical connectors as USB-C cables, but is a different – and faster – protocol. If you want to use the cable with Thunderbolt accessories, you’ll want to make sure it is compatible.

The wiring is the same, so you don’t necessarily need a Thunderbolt-specific cable, but with standard cable the speed will drop off over longer distances. A decent-quality 0.5-metre cable will support the maximum 40Gbps. But if you want to go longer distances, you’ll want an active cable.

The keywords to look for here are ‘Thunderbolt 3,’ ‘Active’ and ’40Gbps.’ These cables are significantly more expensive than passive cables, so keep cable runs short if you can. Oh, and active cables are an exception to the rule, and don’t support USB 3, so should only be used for Thunderbolt devices. Effectively these are Thunderbolt-specific cables that just happen to use the same physical connectors.

Jeff Benjamin contributed to this piece.

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