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Modding a power supply into a test PSU is one of the easiest and inexpensive mods that doesn't require a lot of experience. Anyone from system builders to PC technicians can benefit from this tutorial, as can anyone that wants to gain modding experience before moving on to bigger and more complex projects. Best of all, this is one of the few guides we know of that doesn't require opening the unit. Even when unplugged, power supplies hold enough juice to shock or kill a person, which are surefire ways to ruin someone's day. And speaking of fire, be advised that once this mod is complete you shouldn't run the unit for more than about 5 minutes a session, plenty of time test a component. What we'll be doing is fooling the PSU into thinking it's connected to a motherboard so it can work as a standalone unit, and power supplies have a tendency to overheat if not enough electricity is being dispersed.
There's not a lot of materials needed for this project. The short list includes a wire cutter, a wire stripper (I use needle nose pliers), a working power supply (AT or ATX), and electrical tape or heat shrink tubing.
To get started, locate the main 20 or 24 pin ATX connector, which will be the largest one in the bunch. This is the one that would normally connect to the motherboard.
If using an AT power supply, there are two main connectors instead of one larger one, as seen above.
In the bundle of wires coming from the large ATX or AT connector, find the green wire. Directly to the left of the green wire will be a black wire. These are the ones you will be clipping. Note that on an AT power supply, the green wire will instead be orange. Go ahead and clip the green (or orange, if using an AT power supply) and black wires as close to the connector as you can. Strip the ends of these wires and twist them together. When tightly wound, close it up with some electrical tape or heat shrink tubing.
And that's it, your power supply mod is complete. To verify that it was done correctly, connect a working optical drive or other component and fire it up. Congratulations, you now have yourself a working test power supply!