[elihu]

Low-voltage DC for long wire runs is kind of wasteful -- you either lose a lot of energy in the wires or you need extra thick cables, so I wonder if the best way to do this is to have a high voltage line (AC or DC, it doesn't really matter) that goes to an outlet that has its own self-contained switching power supply and a bunch of low-voltage DC outlets.

Transitioning to this sort of system would actually be simple, you'd just have to make DC power supply boxes that plug into a regular 110 or 220 AC outlet -- sort of like multi-port USB power adapters, but designed for more power and probably higher voltages: perhaps +/- 12 volts and ground.

A more sophisticated system might be that the DC power supply can supply a different voltage/current to each port, and it negotiates with the device to supply to current power. (I think this is basically how DC fast chargers for EVs work -- the car tells the charger what it can accept, and the charger supplies that the car.)

Maybe "dumb" devices that don't know how to do the handshake just default to 5v DC or something.