My suggestion many posts back about using a barrel jack was somewhat sarcastic, or something, not sure what the right word is. But the basic point is this: If that goal is simply to decide on a common power port to use on all portable devices, then any USB port, in fact, just about any data port, is a poor choice. A common barrel jack is obviously superior from a mechanical and functional standpoint.
Oh wait, the USB C standard allows negotiation for multiple different voltages and max currents. Then I remembered a universal laptop power supply that I once owned. There was a selection of adapter tips that plugged into the end of the cord going to the laptop. Inside each adapter was (I assume) a pair of resistors that returned a reference voltage to the supply. This made it possible for the supply to provide any regulated voltage required in order to serve owners of laptops from different companies. So I tossed that out for everyone to chew on, and some of you did some chewing.
Obviously (I hope it's obvious) an analog feedback signal would not be a good solution moving forward, but it does highlight the fact that something as sophisticated (and fragile, and expensive) as USB C is not required if all you want is a common power port.
But, I also don't believe the goal is simply a common power port, so there you go.
EDIT: I do have serious concerns about the durability and lifetime of a USB C port when plugs are repeatedly inserted and removed, multiple times per day on the same device. The laptop I'm writing this on uses USB C for power, and it has generally been trouble free, but the simple fact is that the jack is a little more loose than it was when I bought the computer a year ago. The USB C power cable can often be seen hanging off the jack a little bit sideways. I push just push it back in. But, the fact is, the laptop has plenty of room for power jack intended just for power that would be far better suited to the job. This has nothing to do with laws. It's just an observation.