Power Delivery is a negotiation, not a speed

Before Power Delivery, a USB port offered five volts and the device took what it could. PD replaced that with a negotiation: the charger advertises what it can supply, the device asks for a combination it can use, and they agree. Everything modern about charging follows from that handshake.

PPS, Programmable Power Supply, is an extension of the same idea with finer control. Instead of picking from a short menu of fixed voltages, the device can request small adjustments as the battery fills. The practical benefit is less waste heat, because the charger delivers closer to what the battery actually wants at that moment rather than something nearby.

The catch is that both ends have to participate. A phone that wants PPS and a charger that only offers fixed PD steps will still charge, just not at the speed either was capable of. A phone built around a manufacturer's own protocol connected to a charger that does not implement it will fall back to something basic and slow. Nothing warns you; it simply takes longer.

This is why a listing that names a protocol is more useful than one that names a wattage. "PD 20W" is a sentence with two facts in it. "20W" is a sentence with one, and the missing fact is the one that determines whether the twenty watts is ever reached. Samsung's faster charging mode and the 25W figure that accompanies it is another example of a named behavior rather than a bare number.

None of this lets anyone predict a charging speed for a particular phone. The result depends on the phone, the cable, the protocol both ends support, and the temperature of the battery at the time. Any listing that promises a specific number of minutes to a specific percentage is describing a test, not your morning.