Pdsink: USB Power Delivery Sink library for embedded devices

One big issue that came up (and killed the idea) is that if you are not battery powered, then putting a USB-C power input on your device that will only work if you can negotiate 12V+ with adequate current will just cause confusion. In my case, I don't think I could even boot to an error message on 5V.

Phones and the like don't have this issue, since they are still usable (charging slowly) on 5V, but can make use of higher voltages and currents to charge faster.

So I guess my question for the implementer is how booting & negotiating on 5V and then accepting higher voltage is likely to work in practice.

That's not to say that a boost converter doesn't have value, but it still leaves a gap where there could be confusion.

The confusion or complexity even multiplies if the device has additional USB-C for data transfer. In that case, you either have to mark one port as being the "power in" port, or you have to support power in and data out on all the ports, which gets complicated and expensive.

It would be a great move by the USB IF to think through this sort of thing more carefully. Right now the USB-c connector is so overloaded in terms of power, display modes, thunderbolt, speeds, etc. that it's very hard to predict whether two USB-c devices will connect and at what power or speed and with what capabilities. For power, it would be helpful to require supplies to have a standardized status LED so that e.g. green means that the supply is providing the highest power allowed by the device (not the supply), yellow means there's been a compromise, and red suggests an error condition.