Depending on the PC model, these are rated anywhere between 150 and 240 W. For supplying socket 7 main boards they have four different output voltages of +5 V, +12 V, -12 V and -5 V.
They are mainly primary switching power supplies with power switches arranged in a half-bridge configuration. The outputs can drive the usual 20 A (+5 V), 8 A (+12 V) and 0,5 A (-12 V, -5 V). At approx. 205 W output power and a typical efficiency of 75 % this means a dissipation of only 68 W. I had acquired an unbranded PC power supply, measuring 140 x 100 x 50 mm (W, D, H) and weighing 350 g. Most power supply units are designed according to the same principle (half-bridge configuration) and hence the following described modification should be applicable also to power supplies from other producers.
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