If you can *blow* a electrical circuit just by plugging a hoover in, it's far, far, far too close to the wire for a server to run on.
If she'd *unplugged* something, yes, sure, but... again... if you need people not to unplug stuff, lock the plugs away inside a cabinet and/or put a great big sign on them.
We might all validly blame the cleaners etc. at one point but I can't expect a (probably) minimum wage employee who gets into trouble if things are dusty for not plugging into a perfectly valid outlet that doesn't have any warnings on it (even "NOT EVEN CURRENT TO RUN A HOOVER!") and trying to do her job.
This is as much on IT as it is on the people responsible for physical access, and the cleaner is pretty blameless. They took reasonable steps to do their job and weren't ignoring any signs, warnings, etc. presumably.
Honestly - you've got a big-arse server and you let people have open access to plug sockets (e.g. if you had a UPS you would *NOT* expose the UPS-backed plugs!), and those plugs aren't capable of running... what? Another 1600W? What the hell kind of electrical wiring do you have.
I'd also like to point out that in the last four years I have complained and got a direct feed to IT for exactly such issues... except we weren't within 1600W of killing the circuit, but within 10KW of killing the site (forcing us to upgrade the main transformers out in the road, not just the internals). But I had phase-crossing devices (shouldn't even be possible!), people flipping circuits further up the chain, people kicking out cables under their desks, etc.
If that thing is important enough that you have to lock the door, it's important enough that you have to stop every Tom, Dick and Harry who does get access (fire alarm engineers, access control engineers, etc.) from plugging their test equipment in. Which means big-ass signs, covering sockets, or simply not having them were people can get in.
Literally, guys... a pack of baby-proof plug protectors and a label printer... how hard is that? You can even get covers for rocker switches to stop you turning them off. Not to mention, anything of value should be on a UPS, which means that it goes bananas when you turn its feed off, but gives you time to turn it back on, and the UPS-protected sockets should be in a big-ass locked rack away from cleaners and casual "I'll just plug my 220V->110V convertor for the drill in here" workmen.