Protection circuits in SMPSs. Snubber and SCR commutating circuits. My frequency is 800kHz. In this time, the voltage rises from 0V to Vpeak, for the rise time the steep beginning is the point to view at. Now lets look at the AC-voltage.
Duty cycle is low, so the derating due to thermal problems is negligible.
I apply 10kVrms, this is factor 1.5 above the specs. Now on to the DC-voltage. 20 Caps in series with permissible 1000Vdc are 20kVdc total. All in all, I drive them too hard, yes. But considering the fact that a typical hobby coilers system will run not more than 1 hour every weekend for max.