Controlling high voltage/current signals with a Pi function generator
I use cascaded string of R dividers for regulating feedback for &lt;25kV and capacitive dividers for feedback of regulating the primary up to 1GV which is done by several companies incl. Chinese and ABB.  Since both caps charge up during power on the voltage DC or ac ratio is based on C ratio.

CUrrent and voltage sensing can be at suitable stages in primary and on DC supply for arc detection, and fault protection.  Partial Discharge sensing is advised when contamination is an issue on insulation.  DC ratings must be derated from BIL ratings for lightning surge due to ionic contaminants.

Marx generators are the typical mode for generation of UHV low power, using leather friction belt motors and stepper actuated gaps to,parallel charged caps and triggered by a pulse to make all the spark gaps as a series switch for each cap. I have used these up to 200kV for testing, using two well cleaned BIL200 bushing insulators for both impulse and DC.

For very low currents like on non-ionizing LASER Lexmark printers, I developed a resonant stepup XFMR oscillator using LM358's with R feedback and PWM control from +/-15kV within 1% with no shielding required for $15 BOM cost in volume