Well, uh, AC vs DC and 100-250 volts versus 5-48 volts are two completely different dimensions to the problem here.<p>For example, there has been some standardization of high voltage DC power distribution for datacenters, seeing as that could simplify providing battery backup, etc.<p>But back to the residential case:  As soon as you go to lower voltage power distribution, unless you spend a lot more on copper (larger conductors), you&#x27;re really hurting as far as power distribution losses:  your load uses 10 times as many amps running on 12 volts DC as it did on 120 volts RMS AC.  Thus your loss due to the resistance of the wire is 100 times what it was, given the same wiring.  (i.e. the same series resistance -- your loss is P = V * I = I^2 * R)<p>And no, you don&#x27;t suddenly get much greater efficiency in the power supply of the device - a lot of off-line power supply designs today are already 90% efficient, and even if you provide 12 volts (or 12 and 5) to the plug, there&#x27;s going to be a lot of things you want to do in the device that does not satisfy, and if you want <i>exactly</i> 12, you&#x27;re going to need some kind of DC-DC converter with regulation, because you cannot predict how the 12 volt supplied at the wall will go down due to other load at any given point in time -- so just like a laptop has various DC-DC converters from the 18 volts supplied by its power brick to the various internal circuits (Vcore logic, 1.8 volt logic, 3.3 volt, 5 volt USB, backlight circuits, etc) most devices will still have that.  They might not require as much safety isolation, but you&#x27;re not going to get them to be magically far more efficient than what we have today.