- Definition
- USB Power Delivery is the negotiation protocol used over USB-C that allows a power source and a device to agree on a voltage and current pair, rather than the device drawing a fixed default.
This page defines the term. For what it means in practice, see USB Power Delivery and PPS: how to read a charger specification.
What changed
Before USB PD, a charger offered a fixed voltage and a device took what it could. A phone that wanted 9 V had to be paired with a 9 V charger, and the pairing was often manufacturer-specific.
USB PD replaces that with a conversation. The source publishes a list of the voltage and current combinations it can supply; the device picks one and the two confirm it. If the device wants something the source cannot offer, it negotiates the nearest workable combination instead of failing.
Why the negotiation matters
Power is voltage multiplied by current, and the same wattage can be delivered in different ways. A 100 W supply can be 20 V at 5 A or 48 V at roughly 2 A. Higher voltage means lower current for the same power, and lower current means less resistive loss and less heat in the cable and connector.
That is the whole reason the specification keeps adding higher voltage levels as power targets rise. Pushing more current through the same connector is the option that runs out first.