[crote]

This should never happen, provided everyone is actually following the specs.

If a charger outputs X W and a device needs Y W, for any X > Y it is guaranteed to output the voltage and current combination the device requires.

Every <=15W charger supplies 5V @ 3A, every 15-27W charger additionally supplies 9V up to 3A, every 27-45W charger additionally supplies 15V up to 3A, every 45W+ charger additionally supplies 20V up to 5A. A higher-power charger is therefore always a superset of a lower-power one. A charger may offer a variable voltage, but this variable voltage may not exceed the highest fixed voltage it offers. With the right cable, it may offer currents above 3A for lower voltages.

Devices are required to be able to charge from any charger providing at least the device's power rating, and it should even provide a similar user experience. It is not allowed to depend on the optional variable voltage or higher current a charger may offer.

Really, the USB PD specifications are fine. There is nothing wrong with them - except perhaps the fact that they are over 650 pages long. If you run into issues with USB-C charging, it is almost always caused by either the device or the charger manufacturer simply not following the damn specs.