[Chas]

The buffer capacitor MUST be a buffer rated cap with a published rating Dv/Dt rating. Any other cap design will be short lived as the high frequency spikes will breakup a common metalized capacitor and drop its capacitance to zero irregardless of the voltage rating.

Generally, buffer caps either have foil or a very thick metalized design.

These can be found at professional distributors such as Newark, Digi-key and Mouser.