Every "serious" electronics builder needs a lot of different power supplies, different voltages, current etc. Having USB power supplies is nice for variety of devices, but it just isn't enough. I've taken an old computer power supply. It can supply all voltages I need, 12V, 5V and 3.3V. But, using computer power supply taken straight from old computer isn't easy. There should be some sort of converter, control device, so it can be utilized easily.

So I've made mine. It is made of WD hard disk shell, lots of cables, one dual-USB bracket, on/off switch, old food processor multi-switch, crocodile clamps and one solder board. It looks nice (IMHO), it can use different computer power supplies (as they are not fixed) and it delivers variety of power: 3.3-5-12V on clamps, two 5V USB ports and one micro-USB cable.

Step 1: How to Make Yours?

I've coupled all same color wires from power supply, and I had luck to have one dead motherboard at home, so I could salvage 24-port ATX socket from it. Don't worry about connecting 20-port ATX power supply to 24-port socket as I did, because it is standardized (see here)

Wire colors are:

Orange: +3.3V
Red: +5V
Yellow: +12V
Blue: -12V (I don't use this one)
Green: PS-ON (shorted with ground powers PS on)
Black: Ground
Violet: +5VSB (Always-on 5V, I don't use it)
Gray: PG (Power good, PS self-test, I don't use it)

So I've soldered all oranges, all reds, all blacks and all yellows together respectively, to one soldering board, and created "rails" on it. That way I could attach all my connectors to voltage I needed. So both USB ports and microUSB cable are connected to 5V and GND rails, red crocodile clamp isconnected to multi-switch (it has 5 spots, but I use only 3) that is connected to 3.3, 5 and 12V. Black crocodile clamp is soldered straight to GND rail.

Step 2: Rest Hardware

I've added lever switch, for turning on and off, soldered to GND rail and PS-ON port. It sports a guard, so my kids can't turn PS on by accident... I've also added one green LED, for power status. On top I've stick piece of folded plastic sheet, to create place for crocodile clamps, so they don't connect by accident.

One more thing is about to be installed: small voltmeter, so I don't "count" where voltage lever is, but to have easy display of voltage that is in clamps.

Now I have variable power supply, that suits all my power need, and it is easy upgradable with newer and stronger ATX PS.