Well, yeah. But it's not that simple. Basically, the device has to request the voltage and power level that's supplied to it over a compatible USB cable from a compatible power source. I suspect that if there is no communication to the power source it defaults to 5 volts because it assumes a legacy device is connected. So measuring the voltage at the open end of a cable will show 5 volts. You won't damage anything you connect to this kind of source because it has to be told to supply a higher voltage by the connected device if it can use it. So, there is no reason to label anything.
Power rule of USB Power Delivery Revision 3.0, Version 1.2
In July 2012, the USB Promoters Group announced the finalization of the USB Power Delivery (USB-PD) specification (USB PD rev. 1), an extension that specifies using certified PD aware USB cables with standard USB Type-A and Type-B connectors to deliver increased power (more than 7.5 W) to devices with greater power demands. (USB-PD A and B plugs have a mechanical mark while Micro plugs have a resistor or capacitor attached to the ID pin indicating the cable capability.) USB-PD Devices can request higher currents and supply voltages from compliant hosts—up to 2 A at 5 V (for a power consumption of up to 10 W), and optionally up to 3 A or 5 A at either 12 V (36 W or 60 W) or 20 V (60 W or 100 W).[59] In all cases, both host-to-device and device-to-host configurations are supported.[60]
The intent is to permit uniformly charging laptops, tablets, USB-powered disks and similarly higher-power consumer electronics, as a natural extension of existing European and Chinese mobile telephone charging standards. This may also affect the way electric power used for small devices is transmitted and used in both residential and public buildings.[61][62] The standard is designed to coexist with the previous USB Battery Charging specification.[63]
The first Power Delivery specification defined six fixed power profiles for the power sources. PD-aware devices implement a flexible power management scheme by interfacing with the power source through a bidirectional data channel and requesting a certain level of electrical power, variable up to 5 A and 20 V depending on supported profile. The power configuration protocol can use BMC coding over the CC wire if one is present, or a 24 MHz BFSK-coded transmission channel on the VBUS line.
The USB Power Delivery specification revision 2.0 (USB PD Rev. 2.0) has been released as part of the USB 3.1 suite.[56][64][65] It covers the USB-C cable and connector with a separate configuration channel, which now hosts a DC coupled low-frequency BMC-coded data channel that reduces the possibilities for RF interference.[66] Power Delivery protocols have been updated to facilitate USB-C features such as cable ID function, Alternate Mode negotiation, increased VBUS currents, and VCONN-powered accessories.
As of USB Power Delivery specification revision 2.0, version 1.2, the six fixed power profiles for power sources have been deprecated.[67] USB PD Power Rules replace power profiles, defining four normative voltage levels at 5 V, 9 V, 15 V, and 20 V. Instead of six fixed profiles, power supplies may support any maximum source output power from 0.5 W to 100 W.
The USB Power Delivery specification revision 3.0 defines an optional Programmable Power Supply (PPS) protocol that allows granular control over VBUS power, allowing a range of 3.3 to 21 V in 20 mV steps to facilitate constant-current or constant-voltage charging. Revision 3.0 also adds extended configuration messages and fast role swap and deprecates the BFSK protocol.[57][68][69]
The Certified USB Fast Charger logo for USB Type-C charging ports
On January 8, 2018, USB-IF announced "Certified USB Fast Charger" logo for chargers that use "Programmable Power Supply" (PPS) protocol from the USB Power Delivery 3.0 specification.[70]
In May 2021, the USB PD promoter group launched revision 3.1 of the specification.[58] Revision 3.1 adds Extended Power Range (EPR) mode which allows higher voltages of 28, 36, and 48 V, providing up to 240 W of power (48 V at 5 A), and the "Adjustable Voltage Supply" (AVS) protocol which allows specifying the voltage from a range of 15 to 48 V in 100 mV steps.[71][72] Higher voltages require electronically marked EPR cables that support 5 A operation and incorporate mechanical improvements required by the USB Type-C standard rev. 2.1; existing power modes are retroactively renamed Standard Power Range (SPR). In October 2021 Apple introduced a 140 W (28 V 5 A) GaN USB PD charger with new Macbooks.[73]
Prior to Power Delivery, mobile phone vendors used custom protocols to exceed the 7.5 W cap on USB-BCS. For example, Qualcomm's Quick Charge 2.0 is able to deliver 18 W at a higher voltage, and VOOC delivers 20 W at the normal 5 V.[74] Some of these technologies, such as Quick Charge 4, eventually became compatible with USB PD again.[75]
-Hal
