The main problem is a lack of service info - I've been unable to locate a schematic source other than from Kepco, and I recall they asked about $100 for a service manual.
One item of note is that these power supplies have a card edge connector extending from the rear panel. Normally there's a connector that plugs into the connector with certain pins jumpered. If that connector is missing, the power supply will not function. Hence, there's a reasonable chance that one identified as "not working" may just be missing the connector with jumpers. You can download the normal operations manual from Kepco and it has details on the pin jumpers and block diagrams. But no schematic. If you don't care about using the card edge connector for remote analog programming, you should be able to just solder the appropriate pins. (I also recall there may be a 10K resistor used between a couple of pins, but it's been too long since I built a connector up that I could be mistaken.)
Out of curiosity, I asked Kepco for a repair quote - this was a couple years ago - and their answer was a flat rate equal to 50% of the price of a new supply.
Looking inside the two low voltage units I have, the parts look more or less standard. It's all analog and seems to have common garden variety op amps and the like, all through hole types. They should be repairable. Have not had the HV version open, but I suspect it's similar. (The HV model I have uses vacuum tube regulators, and but a later PCB revision has transistor series regulators .)
Jack