For me it was computer power supplies. Doing repairs at Ahmed Al Jabber AB in Kuwait for four months (USAF, '98-9 ... I picked winter on purpose), where power was available in both US 110 and British 220 volt, depending on which part of the base you were in at the time. A few places actually had both operational at once.
We replaced at least three power supplies a week there, mainly due to people not checking whether it was set to take 110 or 220, and plugging into 220 (remember: set for 220v, and if the lights go on, but nothing happens, its a 110 outlet
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) and blowing the PSU. We get the system, and check if it works. If its fried, we cut the cable off so we don't try to reuse it. Of course, this works better if you unplug the power cord
before you cut it.
Coworker calls out, "Yup, thats another dead power supply." and from beind the monitor I was looking at I see the actinic blue-white flash caused by him cutting the power cord before he unplugged it. He Leatherman almost hit the 15' ceiling, and then almost landed on his head on the way down. There was a 1/4" hole melted into the blades of the dikes on it, and the two were spot welded together (solved by throwing the Leatherman at the concrete floor a couple times).
Luckily I learn from others' mistakes, so I always double checked they were actually unplugged before cutting them after that since with my luck it would not go so non-injuriously for me.
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