Another benefit is that these supplies have several wired 12 volt and 5 volt outputs. A custom supply with USB plugs and several cigarette-style receptacles could be constructed.
Be safe. Have fun!
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http://www.instructables.com/id/300-Watt-Linear-Power-Supply/
In the schematic I subbed it for the LT10A04 The diode out of the PSU was rated for 50 amps or something silly like that. You can just see it in this picture it is the topmost left hand part on the circuit board that looks like a power transistor. Between the black and the red wires.
That is the power supply I use for my CNC project. It is a lot nicer than some junky old PC PSU. About the handiest thing I've found with PC PSUs is the metal case itself. I use those more than anything else I've ever salvaged out of a PC PSU. I guess the wire is handy too. It is nice stranded hookup wire. Sometimes I get a decent heat sink out of a PC PSU, most of the time they're those aluminum sheet heat sinks and they're pretty terrible. Other than that the rest of it I've never found much use for myself.