I am trying to replace the power switch on an old emachine tower.

I had to have my power unit totally replaced about 2 weeks ago. You are going to have to replace the entire power unit. I have a Gateway from 2002. I was told at the repair placeI went to by the tech who's worked on every imaginable computer tower for many years that the Gateway I have was built at the height of the Gateway company and is a very good tower. He did say that Gateway was bought out several times and the now Gateway company is the EMachines and that the Emachines are not very good. Too bad I can't send you to my tech guy as you are probably not in Ohio where I am.

Anyway, you need to replace the entire power unit. You'll probably get a better power unit anyway than what originally came with the tower from the factory.