I did that to a Sun Ultra One station once...
About 25 years ago, my US employer provided weather satellite instruments to the European Space Agency, and I did on site ground support, which included setting up the instrument test console; a Sun Ultra One if recollection serves me. The test control room was wired for 220V 50 Hz, and after procuring the relevant power cords with Schukosteckers, I connected the Sun monitor to the mains - having first verified that it was automatically dual-voltage agile, and didn't require a switch.
Alas, I then neglected to verify that the CPU was ALSO auto-adaptive. (The nameplate said 105-230V AC, 50/60 Hz - we checked that before shipping it - so we were good, right?). Plugged it in, flipped the switch, and POP! Oops. Dead, smelly PSU. The CPU DID have a selector switch. which was, of course, still set to 110V.
Fortunately, I had good relations with the local techs, and even more fortunately, the PSU was a standard PC type. We made a quick trip to the local Mega store, where I bought a replacement and swapped it in. Mission rescued. (I think we first temporarily pillaged an idle Sun workstation for its PSU so I could get the console up and running, verifying that the rest of the station hadn't died as well.)
Never made THAT mistake again.
Ironically, some of the other instrument contractors were using 110V-only computing gear, and had a separate AC supply through a stepdown transformer. Which I didn't use, since the Sun station was dual-voltage capable.