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I have bought from eBay this power supply.

It gives 5 V and 12 V to power a hard disk. They sell it together with a IDE/SATA USB adapter. I measure the voltages and they were not proper.

When you adjust R8 or R12 the voltages change. When one increased the other is increased too. as the voltages are proportional to the ratio of winding of the transformer. Also when one is decreased the other is decreased too. It regulates keeping the voltages ratio the same. So it was not possible to adjust both voltages at the correct level as when I fixed one the other was far away. Finally I suspected that the 12V rectifying diode was a 0.7 drop one and it was so. So I changed it with a 1N5822 and adjusting R8 both voltages come at the correct levels !!!.