The particular model is: iMac A1419 Late 2012 27"
My current work includes repair computer parts. It is the third occasion that appears the same model with the same problem !!!
The records of the "no-break" show only a peak of 240 VAC is incredible that a jump of voltage (120VAC to 240VAC) cause the explosion of an SMD Ic.
It is a matter of poor design or intentional failure to bring visits for service?
I leave some photos of the damage below. And some of the specifications and input power supply.
Three units of the most popular desktop computers in the world! Stop the presses!
Anyway, with how closely I follow Mac tech sites, if this were a widespread problem, it would be widely discussed there by now, and it's not. So I would assume it's a local environmental factor rather than a broad design or manufacturing flaw. (Apple has been using Delta Electronics power supplies for decades, and they have a reputation for being unusually robust.)
(Without wishing to offend fans of apple)
Nope, you just immediately included insinuations of deliberate sabotage by the manufacturer to cause service calls. No way anyone could be offended...
Never mind that it'd be illogical for a company to design products to fail
within warranty. (AppleCare is for 3 years from date of sale, so most "Late 2012" units would still be covered by AppleCare right now.) But of course, despite what the conspiracy theory tinfoil-hat anti-corporate crowd claims, nobody actually designs products to fail on purpose. They merely design them to be as cheap as possible
without failing during the warranty period, which isn't the same thing. In any event, Apple products are known for having above-average build quality and hardware longevity, so the argument of deliberate sabotage is a non-starter.
Can be a consequence of fast switching? 120v to 0v to 240v to 120v fastest than a relay can change the state?
Erm, that's not how switch mode power supplies work. The input voltage range is just that: a continuous range, not a bunch of discrete ranges. (In fact, many SMPS's can work on lower voltages than stated, and on wider ranges of frequencies, often down to DC!)