The USB-IF has defined power ratings with each USB version as well as a Battery Charging specification for power adapters. Over the years, the power capability of USB increased substantially from the original 2.5 watts to 100 (see USB Power Delivery
). See also poweredUSB
Version Volts Amps Watts
USB 2.0 5v .5A 2.5w
USB 3.0 5v .9A 4.5w
BC 1.2 5v 1.5A 7.5w
Power Delivery over USB-C cables
PD 5v 3A 15w
PD 9v 3A 27w
PD 15v 3A 45w
PD 20v 5A 100w
See USB power delivery.
USB Battery Charging
When USB Battery Charging 1.2 was introduced in 2010, the following terms were coined to define the USB port's functionality.
Standard Downstream Port (SDP) - Data transfer only.
Dedicated Charging Port (DCP) - The port in a power adapter for charging only; no data transfer.
Charging Downstream Port (CDP) - A port that is capable of transferring data and charging the device at the same time. Also called a "charge and sync" port.