Then if you account for the losses of DC transfer, even 1% more efficient AC-DC converter would be worse, maybe even couple.

You waste slightly more materials to make bunch of small AC-DC converters, but there’s a reason AC is being used for transfers.

AC transfer is way way less than DC transfer, also lower the voltage, higher the amps, and amps get easily lost on the transfer, while voltage does not.

So having in a datacenter kilometers of DC power transfer lines would probably account for a bit of losses on the road, and therefore extra heat.

Having one AC-DC converter per rack might actually work. You could get the most power efficient normal PSU you can find, which would easily power atleast 40 of these. More likely close to 100.

But then the wiring work would take lots of time, unassembling these, throwing away the small ac-dc converters, and running new wire, soldering it up, putting connectors, fuses etc. You would need 1 fuse per device, might very well make this environmentally a very bad idea, and atleast quite costly in employee time. So there would need to be mass manufacturing of these which takes only DC 12V, which still might not be that good idea after you account for all the extra plugs and wire.

Besides, usually smaller tends to be more efficient …

For now, my NSLU2′s server my needs, but eventually it would be nice to have something that could push the bits around at a faster rate.

http://delock.de/produkte/gruppen/multimedia/delock_usb_20_to_svga_adapter_dl-a16v_61540.html