https://www.instructables.com/id/Con...gular-DC-Powe/
In this Instructable, I will show you how to convert a computer power supply into a regular DC power supply with 12, 5 and 3.3 volt outputs. For about $10!
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My 400 Watt power supply can deliver 23 Amps through the 12V rail, and 40 Amps through the 5V. That's very good for something that, aside from the initial cost of the PSU, cost about $10.