Apple 20 Watt USB-C Power Adaptor

fourwheelcycle wrote:

Why does Apple's 20 Watt USB-C Power Adaptor say its 5V output is 3 amps? Shouldn't 20W/5V=4 amps? I assume I am missing something about Apple's or USB's power protocols.

20W can provide a maximum of either 5V3A or 9V2.22A.

Apple USB-C power adapter volts, amps - Apple Community

The 20W Power Adapter has a maximum power output of 20W - but not necessarily at 5V.

Apple’s 20W USB-C Power Adapter supports USB PD (Power Delivery) - with which the Power Adapter can use a higher voltage with devices that support USB PD. This 20W Power Adapter is also capable of 2.22A @9V = 20W

With devices that only support the standard USB 5V bus voltage, the maximum power output is 15W.