And the idiot award goes to...
When I was a lad I used to tinker with very basic electrical/electronic equipment including video recorders (when they used to cost more money in real terms). Friends mum had one that was being skipped as it had broken down, so I got my grubby paws on it.
Pulled out my trusty Voltmeter and tested power on the AC input side of the transformer. Then tested power on the output side. All ok.
And then my brain farted and I connected the Voltmeter *ACROSS* the transformer (1 pin on input, 1 pin on output). Despite previously seeing voltage on the output pins, my brain said something akin to "but is the power flowing correctly through the transformer". WTF?
Amazingly bright flash and a loud bang that left me temporarily deaf for around 5 mins. My glasses caught the main impact of the glass fuse - would have been much worse if I hadn't been wearing those.
That was the last time I ever worked on electronics. Gave me a very healthy respect for electricity.