I have a couple of old power supplies in which Rifa brand metalized paper line filter capacitors (for 240V mains power) have failed – or may fail – like in this question here.
30+ years sounds pretty good for a capacitor, but researching replacements turns up lots of opinions about brands and references to different types and materials.
Similar metalized paper capacitors are still available (Evox Rifa is now Kemet), which though a bit pricey have the appeal of looking like the original part. One downside is their failure is messy!
Alternatively there are cheaper metalized film capacitors with polypropylene or polyester.
Is there evidence for a best replacement type considering performance and reliability?
Best Answer
As user EM Fields already suggested, I have already half-answered your question in the linked EE.SE post. Short answer is: get an X2 or Y2 capacitor (see below), these are almost always MKP (metallized polypropylene) film capacitors. Make sure you use a value close or equal to the capacitor it's replacing. Note that both paper and film resistors have very large tolerances (20% is fairly standard over operating conditions), so it doesn't matter if the value is exactly spot-on.
Your application is mains filtering, which is not a precision or high-linearity application. You do not need to worry about the exact type of capacitor. All mains-rated capacitors have similar performance, and performance is basically only dependent on their capacitance value.
What you do need to worry about is that the capacitor is safe to use. If the capacitor is connected between live and neutral, you need to use an X rated capacitor, I recommend X2 to be compliant with 99% of countries' electrical safety regulations. If the capacitor is connected between protective earth (PE) and live or neutral, use Y rated capacitors.
DO NOT use ceramic capacitors. They have very unfavourable failure modes that can cause fire or electric shock hazard.