On Sat, 03 Feb 2018 12:12:56 +0000, Archibald Tarquin Blenkinsopp wrote:

The switching device would be short in a number of cases and mosfet or
bipolar the cause was all too often the RC snubber network across the
primary. The purpose of it was to remove the high energy spikes which
are a natural result of switching an inductive load at speed.

There's also an LC mains filter prior to the rectifier and that's highly
prone to failure as well. When an SMPS fires up from cold, the initial
surge current can be huge, 'cos it looks like a short circuit at switch-
on.


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