I want to change my power supply so that once it is plugged in it will supply the voltages. I am not too sure how to trace this down. I've GOT one arm behind my back and my power supply unit is split open and ready for disection. If I need to insert a momentary switch this would be fine.

Any thoughts?David Tebera....I really dont uderstand what your ASKING ...a power supply does supply the various voltages required ......or am I missing SOMETHING ?

"If I need to insert a momentary switch this would be fine."  why would you wish to do this ...please explain ?

"I am not too sure how to trace this down." What are you trying to trace down?

A power supply should provide 3.3V + , 5 V + /- , 12v +/-

Let us know

dl65  Ok.
Don't laugh.

I have a lot of spare parts (motors and such) lying around and was going to play with designing my own "Robot Wars" robot, (really just RC).
I wanted to use the power supply (PS) to run the machine until I get batteries to do the job. In other words I want to use the PS as a transformer to provide me the 12 volts while the creation is on the workbench.

I ASKED about a momentary switch as I am unsure what happens when you turn on a computer. I thought the battery sent a small current to the PS which kicked it on. I did not think it to be a constant supply to the PS.

Stupid I know.

(Thank you for asking dl65.)ATX power supplies are ALWAYS on when plugged in.   Pulling one line to ground turns it from standby to full on.  I think it's pin 8 (gray) on the 20-pin motherboard connector.  Connect it to pin 7 (ground).  It also needs a load to turn on.  Slightly older power supplies, with the 2-6 pin connectors are fully on when the main power switch is on.

Computer battery has nothing to do with turning power supply on.  It works very much like your TV.  If it wasn't in standby, the remote wouldn't be able to turn it on.