Really strange SMPS design.

[electronics-whiz]

I took part a SMPS from a storage server from like 2003-04. It had some normal input part, then had the transistors, etc on a separate PCB n a heatsink. Normal SMPS transformer. seems to put out like 52V DC, then this ran 3 DC-DC converter units. 2 in parallel and another. Used 3 small fans to cool two for the SMPS, one for inverter. Seems like a rather inefficient, impractical setup for no real advantage.

[coppice]

A number of server supplies, especially in telecoms applications, are actually 2 supplies in one box. They convert the mains to -48V or so, to charge batteries. They then convert the -48V to the required voltages to run the server. Does your supply have external connections to the 52V section for batteries?

[Howardlong]

I was wondering whether it also had an option for PoE operation? That's 48V.

[electronics-whiz]

I don't have docs, etc on it. It has a small connection that kooks like a ps/2, but more pins. Then another with two wires. All are small like 22-24 AWG. I doubt those could power it.

This is from an old storage area network, I think these units were from the rack units that held all of the hard drives.

[TerraHertz]

As Coppice mentioned, a lot of telecom installations have a system supply of 48 to 50 VDC, which is generally battery backed.
Maybe your unit was designed to have an option of operating in such environments, but wasn't actually configured for it?

Why is it 50V or less? Because they wanted the highest possible voltage to overwhelm line resistance, and 50V is the highest voltage legally acceptable for live hands-on work on equipment.
Why is it -48V and ground? Because that way the telephone land line wires are negative relative to the actual ground, and this helps prevent corrosion of the wires and junctions.