BA23 PDP11/23 Power Supply that couldn't; Trying to locate a

It has the AC mains across it (it's almost certianly conencted between live and neutral of the mains input, possibly after filter inductors). So it cou;dn't be an electrolytic, which are polarised and designed to have DC across them. As to why use a mrallised paper capacitro, I suspect it was the cheapest type that could stnad the voltage and be reliable (OK, it's failed now, buit it;'s been around fro proably 30 years or so). There would be no particualr tolerance requiremnts here. Wht you need to get is a capacitor of the same value that is rated to withstand the full mains AC votlage. Most good components suppliers list capcitors for mains filter applications. Since they're designed for what you want to use them for, theres no good reason not to use one. -tony