We've had a small number of power supply failures (say a dozen over 6 or
700 machines) on 5000/150's, but they tend to be very much an "I'm dead"
problem.  As for checking the power supply, the easiest check would
probably be to just plug a multimeter into one of the disk drive plugs
and see if you get 5V between red and black and 12V between (I think)
orange and black.  I think all DEC power supplies are adjustable - I've
seen DEC engineers play with screwdrivers - but I wouldn't know what to
twiddle with...

Your symtoms maybe sound like a heat issue if letting it stand for a
while seems to make it better - maybe there's a hairline crack on the
motherboard or something like that.  Bit of a coincidence if you're
seeing on both boxes though.  Have you checked that the CPU daughter
board is pushed in securely?

Simon.