I am experiencing power supply problems ( not fuse ) . Is it worth
fixing - how to troubleshoot .

Did you diagnose it to determine whether or not it was the power supply?

It could be a bad power button on the front panel. Simple test to determine
this is to press the disc eject button, the box should turn on and eject the
drawer. Of course, if the power switch is bad you can't turn it off properly
but unplugging it while on shouldn't hurt it just so long as the hard disk is
sitting idle when you do it.

I have seen those drop in psus on the
web put they are kind of pricey . Can I simply bypass the power supply
and hook up on of the many spare ATX power supplies I have accumulated
? Your help is appreciated .

It's possble, but not recommended. It's safer to go with a power supply
designed for your Box, and you have to make sure you get the right power supply
for your version of X-Box. Versions 1.0 and 1.1 use what looks like a single
piece AT power connection while all newer versions look like they use an ATX
type connector.

As for expense, try looking for replacement X-Box power supplies on eBay. If
you can't get one that way, just bite the bullet and buy a proper replacement
power supply. It will still be cheaper to do that than buy a whole new X-Box.
- Reinhart