Re: Resistor in PSU
Usually, it is there to ensure the power goes off quickly if the AC is disconnected. Without it, the DC rail may fall slowly, particularly as the voltage decays to a low level. Slow dropping DC could have bad consequences, particularly for logic circuits. Microprocessors may also need a rapid rise in voltage from zero to initialize properly. The resistor just bleeds some current to ground to make sure the starting point really is zero.
Brian.