I’ve never worked with major enterprise or government systems where there’s aging mainframes — the type that get parodied for running COBOL. So, I’m completely ignorant, although fascinated. Are they power hogs? Are they wildly cheap to run? Are they even run as they were back in the day?
Definitely power hogs. Modern switch mode power supplies are incredibly efficient.
I never really administered anything like that myself but I had a friend who took care of some old servers ~20 years ago in college. Multiple power drops in that small room went to fuse panels rated for several hundred amps each.
Unfortunately all I know were that they were VAX mainframes and were already considered obsolete in the late 90’s ;-)