That seems to make sense. I wasn't familiar with snubber circuits, nor
even the word snubber, until I looked it up now. You wouldn't want the
voltage spike hitting the aircraft when plugging in the outside power,
so that probably limits the rate of voltage change.

I don't think it protects against reverse polarity since it doesn't look
like something that gets replaced easily if it breaks. The parts are
quite small for current limiting too.

Thanks everyone.
I'll put it back in.

Larry Dighera wrote:

It sounds like a surge suppressor or snubber circuit to me.