This is what I use to charge the 15KJ capacitor, it is a 5kv 20ma furnace transformer which is rectified
depending on the application with the 6kv 25ma diode below or with a cascade.
A picture of my variac, it has 2 120vac 1amp breakers which are wired to switch on/off the 120vac
power supply and the other to turn off/on power to the 5kv transformer.