When should a power supply be declared Perma-Dead?

["General_Failure" <tristan.mumford@gmail.com>]

I would scrap at least 4 computer power supplies a year. Mostly from
the instant-fuse-blow disorder. Just recently my apple //e's power
supply has been added to that list.

Initially I suspected the Z80 card, which I still believe may have
started the problem. But now I don't know.
Even with the power supply on its own, not plugged into anything, It
has an instant fuse disintegration. Thankfully not as powerful as the
lightshow a lot of x86 power supplies give.

I can't see any problems with the PCB or components in the Dyna Comp
power supply. Nothing is even remotely suspicious. It actually looks
freshly built.

Should I try tracing the fault, or just give up, steal it's low voltage
cabling and give the apple a PC power supply?

Also, after the first fuse blow, I decided to fit a panel mount fuse
holder. Very convenient.

With AT/ATX power supplies I never bother with trying to repair them.
The apple supply is a bit of a rarity though.