Pure DC (Direct Current) power standard for servers

Hi all – Is there a DC power standard for servers? I mean Direct Current, not datacenters, though the latter figure into the question.

I read that some (most?) datacenters are using centralized DC power instead of converting from AC to DC for every server and switch individually. In other words, servers in such scenarios don't have traditional power supplies. So what do the servers have? What sort of electrical interface is it?

And where do I get the equipment so I can experiment with it? I don't see DC servers listed anywhere, meaning servers with some sort of pure DC interface instead of the usual converting power supply.

I'm also interested in any UPSes that feed DC only to such equipment, rather than the standard NEMA AC plug.

Thanks for your feedback.