The first USB standard for PD, Power Delivery 1.0, was 3 amp * 5 volt or 5 amp at 12 volts or 5 amp at 20 volts for 100 watts. If your power supply or cable is 1.0, you get a max of 3 amp at 5 volts.USB-C cables that the claim are rated for 240W
The second allowed 5 amps at voltages up to 48 which gives you 240 watt. Still 3 amp at 5 volts.
Everything else is non standard or uses the recent option to request a non standard voltage. To go from 3 amp to 5 amp, the source (the power block), the cable, and the requestor (the Pi or screen or phone), talk over a data cable in the USB cable. They start at 5 volt 3 amp. If the request is for something else and the cable can understand the request, the cable can pass on the request and switch to handle the new voltage or amperage. When the power supply receives the request, it has to say yes down through the data cable. Then the source, the cable, and the requestor can all switch to a different voltage or amperage.
The 100 watts, 20 volts at 5 amps, was an easy switch as many notebook chargers were supplying 60 ~ 80 watts at 19 volts. I have 240 watt cables but no power supplies supplying 48 volts and no devices using 48 volts. Those top of the line cables are still limited to 3 amps at 5 volts unless they can switch on the 5 amp wires at 5 volts.
For the Pi 5, the critical part is PD in the source and the cable both allowing 5 amps at 5 volts. For the Pi 5/screen combo, two 3 amp 5 volt sockets work with any old cable.
Statistics: Posted by peterlite — Thu Oct 23, 2025 4:25 am