What are USB PD Power Rules?

A lot of my readers have pored over the USB PD specification for a long time (especially when the Nexus 5X/6P phones were announced) trying to figure out how power delivery works in the new USB world. However, much of the PD specification was defined before USB Type-C, when PD was meant to operate on Type-A and Type-B and a lot of the early concepts have since been deprecated or changed. One such concept that was confusing was “PD Power Profiles.”

Practically speaking, almost no one implemented “Power Profiles” in exactly the same way the spec defined. It had a 5V 2A requirement that confused people because most Type-C PD adapters were 5V 3A.

Looking at the newest version of the USB PD Spec Revision 2.0, V1.2, the section of “Power Profiles” is blank. “This section is deprecated.” Great! So no one has to ever talk about Power Profiles again!

Instead, the newest versions of USB PD have “Power Rules” (USB PD Section 10) which make a TON more sense, and I am pleased to say there are power sources on the market today that implement these rules. You can see the new rules in the table and graph I’ve attached.

Going forward, the new voltage levels to expect on new chargers are 5V, 9V, 15V, and 20V. The 12V level is now optional.

The new rules also introduce a “superset” guarantee. Larger wattage power sources must support all voltage levels below their maximum up to 3A. As the spec says, “Bigger is always better in user’s eyes – don’t want a degradation in performance. Higher power Sources do everything smaller ones do”

As a result, the consumer only needs to know that their device ships with a x watt power supply, and know that any power supply that is rated at > x watts will be at least as good as the one that shipped with the device. When comparing power supplies, they only need to look at the watt rating to know when a charger is objectively more capable than another. Under no circumstances should a more expensive charger charge your device slower than a cheaper one.

I’m also pleased to note that devices that implement the new USB PD R2.0 power rules are already on the market! +Anker's PowerPort+ USB-C PD has a 45W capable Type-C PD port which supports 5V/3A, 9V/3A, 15V/3A, and 20V/2.25A.Their product is available here : https://www.anker.com/products/A2053111

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