Under the USB-C specifiction, without Power Delivery, the maximum power allowed is 15 W. Additionally, the only allowable voltage for Vbus is 5 V. With power delivery, the maximum allowed power increases to 100 W with a maximum voltage of 20 V. A Power Delivery Explicit Contract overrides any other means of determining power levels, as shown in the USB-C spec.

In addition to fixed voltage supplies, there a few other options (section 7.1.3). Variable supplies are "very poorly regulated Sources". Battery supplies expose a direct connection to a device's battery. Programmable supplies expose a well regulated, but adjustable voltage output. Regardless of its other capabilities, any Source must provide a fixed 5V supply.

Side-band Communication

Vendor Defined Messages (VDMs) allow devices to exchange information not defined by the USB specifications. There are structured and unstructured VDMs. Unstructured VDMs provide 14 bits in the header to use for your own purpose, along with up to an additional six objects, each 32 bits long.

Structured VDMs are used to send information about, and agree on, Alternate Modes. For example, under DisplayPort over USB-C, Hot Plug Detect (HPD) is sent as a structured VDM.

Alternate Modes

Alternate modes let you use some of the pins in the USB-C connector for your own purposes. The most common alternate mode is DisplayPort over USB-C. A spec for HDMI over USB-C has also been released. Modes are distinguished with the Standard or Vendor ID (SVID), a unique 16-bit number assigned by the USB-IF (section 6.4.4 of USB-PD spec).

For a full featured cable, you can reconfigure the four SuperSpeed pairs and the Side-Band Use (SBU) pair. If the device has a "captive cable" (cannot be unplugged) or has a "direct connect application" (plug orientation is otherwise assured), three more pins are available. These are the two pins opposite the USB2.0 D+/D- lines and Vconn. You can learn about the connector requirements in section 5.1 of the USB-C spec.