[stephen_g]

Line losses through the cables are usually a killer with really low voltage DC (like 5V or 12V), so I think that AC would be more efficient there.

But some datacentres are using 48V DC now and then just piping that through a switching regulators in the servers instead of going from AC to DC. That could be workable.

[teh_klev]

48V DC has been in multi-client data centres (Telehouse, TeleCity etc) for years. It's a standard voltage in telecoms kit. The data centre I was involved in building out back in 1999 got this as standard.