USB-C might be that DC standard. It is easy to install aftermarket AC outlet modules with an embedded transformer feeding a pair of DC sockets. One could easily imagine a house wired with such USB power outlets, lacking the AC sockets - they'd presumably be supplied by buck converters from some higher bus voltage, likely 48v.
There are outlets with USB-A and USB-C ports. I don’t think there are any with USB-PD because chips are expensive for that. It would be possible to have multiple ports and no AC ports.
But problem is places with lots of devices, then would need power strip and might as well use AC one.
The problem is appliances that draw too much power for USB-C. They also draw too much power for 48V DC. There isn’t any advantage to switching the wall voltage.
> I don’t think there are any with USB-PD because chips are expensive for that.
Leviton makes a 60W unit now that supports PD. Be warned it's a little janky in that it tries to be "smart" and re-negotiate (well, outright drop to 5V) the port if your device stops drawing substantially less current than requested. This can confuse some devices - especially those without batteries. Otherwise I can say the 20V/3A profile works fine on my macbook.
I installed a few outlets last year which claimed to offer USB-PD at 18 watts. They were certainly more expensive than any other kind of receptacle, but not so much that I remember what I spent on them.
I don't think anyone would switch the wall voltage altogether; not in one generation, at least. But a majority of the devices we plug into AC outlets these days convert that power to DC before doing anything with it, and a majority of those devices do so using USB; so one could imagine that a house which had solar panels and batteries could also have DC power wiring and dedicated USB-PD receptacles, skipping the inverter and all the rectifiers.
The majority of devices might be USB powered, but the majority of energy use is from large AC appliances. USB is solved by adapter or special outlets.
Also, the DC voltage for house wires and batteries need to be much higher than USB voltage so will need conversion. Might as well have it be AC to DC converter.
There is a problem connecting solar panels to batteries and needing two inverters. But that could be solved with higher voltage DC between them.
A 48V dc circuit over a 12 AWG wire would provide less than 1/2 the wattage (power) available in a typical 120V AC circuit. You’re still going to need some circuits that can deliver 1500W to power appliances, space heaters, window AC, etc.
