This is a very simple way to make a pretty decent, but cheap benchtop power supply out of mostly old PC parts.
I work for a pretty small computer company, and we end up scrapping a lot of old PCs with tons of still working parts. Getting 'old' power supplies and hard drives is free, as they are typically considered trash. So, finding myself in need of a power supply, I figured this would be a fun weekend project and would put those old parts to good use.

Step 1: Gather the Parts

Things you'll need:
· Working ATX PC power supply
· Large laptop power brick or project box about the same size
· 6 banana jacks
· Switch
· Green LED
· 100 ohm resistor
· Strong double-sided tape
· Velcro with sticky back
· Heat shrink tubing or electrical tape
· Hotglue gun (w/ a glue stick)
· Soldering iron (w/ solder)
· Drill
· Set of drill bits
· Saw or dremel
· Razor knife
· Phillips and regular screwdrivers
· Wire snips
· Wire strippers

Step 2: Breaking Open the Brick

If you decide to go with a project box, this step can be skipped.

Start with clamping down the laptop brick and cutting the cords off.
Next, cut along the seam all the way around.
Then pry the two halves apart and pull the insides out.
Finally, drill a hole where the wires for the power supply will feed through.

I live in an apartment with neighbours, so power tools like my Dremel are out of the question. I went at it with hand saw and a miter block.

Step 3: Prepping the Power Supply

Unscrew and open up the PC power supply.
Snip off all of the plugs.
Separate the wires you'll need plus a couple of spairs from the ones you don't need.
I needed five ground (black), one 12V (yellow), one 3.3V (orange), three 5V (red), the Power Supply On (green), and one extra of each.
Trim back the extra wires. Trim as many as you can level with the pcb. The others you'll have to leave some length to tape or heat shrink.
Close up the box and screw it back together.

Step 4: Start Piecing Things Together

Now, make sure things fit and all of your holes line up. If there are extra tabs hanging off the power supply, like mine has, drill a hole to match in the brick to help hold it in place.

Stick your double-sided tape on the power brick half with the hole for the wires.

Thread all of the wires through the hole in the brick and press it firmly to the power supply. (Glue or screws could work here, too!)

If you had any useable tabs and did drill a hole, put a screw through it to hold it on.

Step 5: Making the Faceplate

Use a pencil or marker to mark the holes for the banana jacks. I had two sets of four, which made things pretty easy to line up. Also be sure to leave room on one side or the other for the switch, wires and any extra parts you want to add later.

Drill all of the holes for the jacks and fit them in place. You could glue or screw them in place if they're like mine. I actually melted the pegs on the back of the jacks to the holes in the brick.

Step 6: Wiring Things Up

Solder the green wire from the power supply to one lead on the switch and one of the black wires to the other lead.

Next, solder the resistor to the lead on the flat side (negative) of the LED.

Solder one end of a scrap black wire to the other lead of the resistor, and the other end of the wire to the lead on the switch connected to the black wire of the power supply you solder previously.

Now solder one of the red wires from the power supply to the lead on the round side (positive) of the LED.

Finally solder in the rest of your red, black, orange, and yellow wires from the power supply to the back of the banana jacks.

Plug in the power supply and test all of your connections. When you flip the switch, the LED should come on and all of the jacks should have power/ground.

Hot glue all of the connections and tape or heat shrink all the wires.

Step 7: Closing the Box

Now, cut a few pieces of the Velcro tape in half length ways and stick them on either side of the brick, so they follow the seam.

Holding the two halves of the brick tightly together, take strips of the Velcro the same length as the last few and stick them over the cut ones to hold everything together.

You could glue or screw the two halves together, but I'd rather always make things that I can take apart pretty easily.

Step 8: Enjoy Your New Power Supply

So now that you have a fairly stable and efficient power supply, you can use it to test circuits or power projects. Depending on the size power supply you use, you could power quite a few projects at once.

It would also be kool to add extra features like an ammeter or a couple potentiometers.