They typically use a standard bridge rectifier..available at Radio Shack (or use to be) for about $5.
Its a very simply 110vt input...through a bridge rectifier and out to the magnet. Some..some have a transformer inside to bring 220/440 down to the proper voltage.
Mine has an additional transformer...or rather a different transformer with voltage taps that are selectible through a rotary switch. Switch Pos 1= 25 volts, 3 is 50 volts and so on.
Some..some have a second switch or switch position..it shoots 90-110 AC through the magnet to demagnitize the part AND the magnet.
These fancier mag power supplies typically have a 90 vot power supply that provides clean DC, rather than 60 hz half wave DC.
Most of the standard version..are very very simple inside. Simply check if you are getting power in, power to the rectifier, and DC out of the rectifier and power to the output of the power supply. Some use a relay instead of switching the entire power supply off and on.. So check to make sure power is going to the relay, power off/on to the relay coil (from external switch) and 90vts dc coming out of the relay.
Ive fixed a shitload of them over the years and its typically a bad wire, a bad switch..then a bad rectifier..and then a bad relay.
If your power supply is old..and it has a selenium rectifier..and its bad...and it is likely to be..simply replace it with the Rat Shack bridge rectifier.
Gunner
"The socialist movement takes great pains to circulate frequently new labels for its ideally constructed state. Each worn-out label is replaced by another which raises hopes of an ultimate solution of the insoluble basic problem of Socialism, until it becomes obvious that nothing has been changed but the name. The most recent slogan is "State Capitalism."[Fascism] It is not commonly realized that this covers nothing more than what used to be called Planned Economy and State Socialism, and that State Capitalism, Planned Economy, and State Socialism diverge only in non-essentials from the "classic" ideal of egalitarian Socialism. - Ludwig von Mises (1922)