All of this??
So you can convert it back to something around 12-18 volts to power the computer that is the size of a laptop.
Yes, many things run from low(er) voltage DC in these days of solid state devices. Just look around your desk and see. There are lots of "wall warts" of varying sizes needed to power everything. Now this doesn't include charging your Nissan Leaf, or Tesla roadster, but many things just use the 120/240 volts mains to get from point A to point B. The actual use is another matter.
OK, there are some exceptions, like the refrigerator and the clothes washer (they have motors!) but not much else.
The big problem with lower voltages for power distribution is that a voltage drop of 1 volt is significant (it is not at the higher voltages). With more current these add up to a bunch of heat (and melted insulation if you aren't careful).
Oh, don't forget: 400+ volts of DC is not very "user friendly".