When the power supply for my Belkin USB 4 way crossover went belly up I needed a +5 volt supply capable of outputting a minimum of 2 amps. An old 12 volt car battery charger could easily power an LM323 3 amp 5 volt IC but it would take a week to get it. The biggest wall-wort I had was .700 milliwatts.
Enter my old power supply from where I found it under the bed. In addition to providing me with a high current +5 volt supply it gave me a high current +3.3 and a +12 volt supply as well. All I needed to make it work was a load on the +5 PSU bar provided by my Belkin but any +5 volt resistive/inductive load, such as a case fan or a 10 ohm, 10 watt resistor, will do.
Step 1: Okay, so you to have an old power supply but not a Belkin or other device in need of +5 volt power so now what?
Try using an old but still working case fan. If you have the power supply you are bound to have one of these. Otherwise you can find them online for about $8 plus shipping. You can also use a 10 ohm, 10 watt resistor or maybe one that is even smaller for less than $1. To find out you'll have to experiment.
Why do you need a case fan or a resistor anyway? Well its because the circuit shuts down unless it has a load. How come? Its probably because the circuit can detect a no-load condition and is designed to shut down when it does. Most switched power supplies need a load in order to operate. When the Belkin or the power resistor or case fan is removed or if the output lines are shorted the circuit will shut down as the result of the internal circuit. One of the great things about using a PC power supply besides the high amperage available is that it will force you to reconnect the load or to remove the short circuit before it will restart after removing and reinserting the line power plug. That's a great safety feature that can save you lots of other trouble.
The case fan shown below is rated at .12 amps and 12 volts or 1.44 watts. .12 amps on the +5 volt bar represents a load of only .6 watts and apparently .6 watts is all you need to tell the PSU shutdown circuit a load is connected and there is no need to shut down the PSU. Now for the connections...