I needed a power supply for my Yaesu mobile. Often times, such as when programming, I find myself wanting to power up the radio in the house. However, since the radio is designed to run in a car, it wants 12 volts DC. 
To maintain flexibility, I've wired the Yaesu with an Anderson connector, and built a cable to plug into a car cigarette lighter socket. This allows me to drop it into a car easily. For use inside the house, I have a power supply from an electric cooler, which plugs into the wall and supplies 12 volts to just such a socket.
However, this power supply isn't up to the task of supplying the current necessary to drive the radio at full power; I can turn the radio on and program it, but if I try to transmit at anything above minimum power, the little power supply shuts down.
Now, lucky for me, a computer power supply can also supply 12 volts. And depending on the unit, it can supply quite a lot of power. But you can't simply plug a radio into a computer power supply.
For starters, the plugs don't match. The power supply has many special connectors for the computer motherboard, drives, etc., while the radio uses a different connector. (in my case, an Anderson SBS connector that I'd scrounged.)
Secondly, while this power supply is able to deliver 10 amps on the 12V rail, none of the components connected to it need that much current all by themselves. Thus, the power supply has several 12V wires going to different places. The radio, on the other hand, wants that 10A all to itself, which makes these little wires less than optimal, (and probably a fire hazard.)
And finally, there are a lot more wires than I need. The power supply can not only deliver 12V, but can also deliver 5V and 3.3V, for other uses inside a computer. The radio doesn't need any of these other voltages.
This is a power supply I rescued from a computer destined for the recyclers. The first thing I needed to do was remove the rat's nest of wires hanging out the back. To keep things clean, I wanted to desolder everything from the board and replace it all with a single Anderson SBS connector. Fortunately, the holes in the board are large enough to accept the 10 guage wire that's on my connectors; the challenge was finding a soldering gun large enough. The wires themselves will carry heat away from the joint, so you need a gun large enough to put heat into the joint faster than the wires can carry it away. A torch would do the trick, but it would also burn the board.
Once I had removed all the wires, I soldered the Anderson connector onto the board. There's just enough wire to carry the connector outside the case, where I could bolt it to the chassis (as a strain relief.)
The next task was to provide a way to turn the power supply on. This is an ATX power supply, which means it's normally controlled by the computer. The computer is able to turn itself on and off, but it also means that there isn't a switch on the power supply; there's no way to turn it on unless it's connected to a computer.
Well, a little research on the internet showed me that if you tie one of the wires to ground, the power supply will come on, and breaking that connection will turn the power supply off. So I drilled a hole in the back of the case, installed a toggle switch, and connected it between this lead and ground.
This power supply is able to drive my Yaesu at full power (75 watts) without any problems. It supplies just a shade under 12 volts, which is less than the car, but the radio doesn't seem to mind. 
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