Power supplies...do the go out slow or all at once?

Wondering if u guys can tell me if power supplies go out gradually or all at once?

I have a Fanuc OM kitamura...

If I try to turn it on cold...I get nothing other than a click from the back

If I hit the power supply with a hair dryer for a second...it works perfect...

Problem is the fan cools the supply and shuts off machine right afterwards....


Anyone ever heard of this...can a power supply be bad and still semi work?