How to select the pulse capacitor?
Having personally tested a variety of capacitors for surge simulator I was surprised to find that only Polypropylene film capacitors would stay cool instead of burning up from intense ultra-sonic power used for surges and in another fixture for electromagnetic tempering of steel bolts. They were often used to block a DC bias voltage or as high-pass filters to stop LF harmonics.

Polyethylene, Mylar and bi-polar electrolytics all failed by overheating and shorting out or by out-gassing material. Other than huge oil-filled capacitors for laboratory use I have found none more durable under stress than Polypropylene film. This is with the understanding that the AC + DC peak applied to the capacitor was no more than 66% of its rated DC voltage.