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-48V.

I'm trying to find out why negative is used, but the answers seem to vary a lot...

I've always been under the impression it was corrosion related.

This is my understanding as well. I believe the effect is called cathodic protection[1].

[1] https://en.wikipedia.org/wiki/Cathodic_protection

48V and DC power is ok for low amperage stuff like telecom. But powering servers takes a lot of watts. So the only practical way to do that would be to power a rack with high voltage AC (120/240/400) and then have a single AC-DC and supply servers in the rack with DC. The battery systems described in this article would have to be single per rack in this configuration.

Until the industry started getting making new DC-DC power supplies with batteries.

Running of DC is how Telecoms Exchanges (central offices) have run since the year dot.

So this is not exactly a new discovery.

So, the Telecom companies created a time travel device went forward to 2015 and stole Microsoft's innovation :)

No of course not must have sent the machine back pre ww2 and nicked a lot of TI's (technical instructions) from the GPO / Bell