I'm in the beginnings of designing a high voltage (<600VDC) power supply to measure leakage of capacitors in tube radios. The idea is that you apply a high voltage to the capacitor and measure the leakage in microA.
I've found a suitable transformer for the project that's 230VAC/400VAC and 50 W, which should give me around approximately 100 mA on the 400VAC winding. If I got the math right I'd be looking at 560ish VDC after rectification and filtering.
Now, I'm trying to figure out how to do the voltage regulation of the output. I don't really need it to be variable, I can live with around 10 steps just below the common ratings of capacitors, as I don't really need to test them exactly at the rating (a cap that leaks probably is going to leak at 400V even though it's rated at 450V). Also, the exact voltage isn't that critical either, 5 volts precision is probably fine.
What I've seen online some people seem to use a N-channel MOSFET for the arrangement, like this one by Mr. Caldeira
I'm thinking of replacing the pot with a rotary switch with different resistors, which begs the question what will happen in a brake-before-make scenario, if the gate doesn't see any voltage it should just stop conducting right? Any recommendations on suitable MOSFETS?