Does anyone know if all ATX power supplies will work with Asus mobos?

As long as it is a standard ATX supply with the correct pinouts for the ATX
feed plug, it will work. Asus and Soyo makes stuff that conforms to the
industry standard, while Dell is far more proprietary than that. (One of the
many reasons why I opted to build my own computer rather than buy one from Dell
or Compaq.)

Whether or not it will work reliably is a different story.

Go get a new standard ATX power supply and try it out. If it doesn't work, you
can always return it to the place of purchase.

Unlike the original Soyo power supply the Compaq doesnt have a power switch
on it

And what kind of power switch are you talking about? A rocker switch on the
back of the power supply module itself or a long black cord with a locking
pushbutton switch on it?

If it's a rocker swtich on the back of the module itself, then that's likely to
be okay. Some ATX power supplies have this switch and others don't.

If it's the latter, then are you sure it's ATX? - Reinhart