Comment by tgsovlerkhgsel

If I remember correctly, some kind of highly efficient (and low cost) voltage halver (not sure if this design or a different one) is AFAIK used with the PPS ("programmable power supply") protocol to let phones charge efficiently:

2x the battery charge voltage is requested from the power supply, e.g. 8.6V if the phone is trying to apply 4.3V to the battery. This way, the phone doesn't need to run any complicated and heat-generating voltage regulation, just the halver, while still being able to request more than the standard 5V over the cable (allowing it to draw more than 15W of power over a standard cable).