[quote name='hubrad' timestamp='1389273047' post='2332164']
Another frighteningly common occurrence is the outer insulation of a mains cable no longer being held in the clamp in a plug..
[/quote]
It's becoming less common due to the requirement to supply moulded plugs on leads.
We hired a snow machine for a gig at Xmas, which was delivered with an IEC lead with a removable plug, covered in current PAT stickers. We plugged it in, and it tripped the circuit breaker on the socket AND the main breaker on the entire building supply. Cause was a short inside the plug. I think commercial companies hiring out gear should do better, personally.
I've had conflicting stories about whether it's even possible to test things like laptop power supplies. At work, the technicians never did these because they said there was nothing that they could test. The last bloke who did our band gear (required for a gig) insisted on doing them, maybe because he was charging per item.