In theory, the PSU in the computer only needs to do half the work when converting 400VDC to 12VDC/5VDC/3.3VDC (lower voltages are converted on the mainboard these days). the SMPSUs used now step the voltage up so the AC to DC conversion is done around 340V. Then the 340VDC is stepped down.
Still, by distributing DC to the computers, the AC to DC conversion has to be done somewhere. You still have all those conversions to do. So unless some particular kind of conversion can be done more efficiently at some particular voltage, it may not matter.
And this doesn't eliminate the PSU in the computer. It just makes it smaller. You're not going to feed that 400VDC straight to the mainboard and do the 400 to 12 step there. My idea completely eliminates the PSU box in each computer, allowing more other parts to be put into the same space ... in exchange for a center whole-rack-serving SMPSU.
So is 400VDC any better than 400VAC or 480VAC? I really don't see that. The conversion near the computer has less to do, but the conversion still has to be done, somewhere. At best, that would be a minimal efficiency increase. And I see a lot of new issues with such a hefty DC running around the place. The advantage of using 400VAC or 480VAC (make that a full ranging 380VAC to 480VAC) is that it allows the use of industrial-commodity distribution components, and is safer for non-electrician computer personnel to be around (pulling plugs and stuff).
How much are those 400VDC breakers going to cost compared to a 480VAC breaker?
