Here's a good example of what we often talk about on here with regard to electros that are normally powered all the time, or at least every day, and then fail immediately, after a period of non use.
One of my bench irons, is a temperature controlled Antex station with a 50 watt handpiece. Up until when I went away on holiday a couple of weeks ago, it was on every day for 10 or more hours, and worked perfectly. Monday morning, after returning from 2 weeks away, I stumbled jet-lagged and grumpy into the workshop at 9am and switched the benches on. The display on the Antex was going berserk, with the temperature figures flickering and flashing. The up / down and menu buttons did nothing. So, first and much un-needed job was to find out what had gone wrong with it. When I opened it up, there was an unexpectedly complex board inside (considering that this is not an expensive tool), and there, right by the side of a regulator on a heatsink (where else, of course ... !!) was a 470uF 40v cap. It looked physically ok. No discolouring of the sleeve, no leakage of electrolyte, and no bulging, but when I ran the ESR meter over it, it went over 40 ohms.
A new cap of course cured the problem. I guess with its location being next to a hot component, it had been on its way for some time, but it didn't get to the point of causing any actual trouble, until it had not had volts across it for a couple of weeks.
In this particular case, it was merely an annoyance to have to repair it before I could start work. No damage had occured because the circuitry in the power supply is all linear. However, it lets you see how these cascade failures in switchers occur, when people power down their DVD player or whatever to go on holiday, and then when they come home and repower them, magic smoke gets released ...
Arfa