[Argus25]

The question what to replace them with I think is fairly simple. Simply avoid X2 capacitors that are constructed from metalized paper. As long as they are some type of other poly cap, like MKP etc they will be just fine and if you get the ones that are "X2" rated, you know they are compliant with modern safety standards.

However, it might be easy to forget, before these standards specifying the X2 capacitor existed, manufacturers who wanted to put mains suppression capacitors on the mains power inputs to their radios & TV's etc, just used standard parts, either oil filled, mica or ceramic types, even seen waxies. But what they did was use 1000v or 1500v parts and so, they practically never failed.

You could expect a modern 240V AC rated X2 cap only to be good for very roughly 600V DC, but certainly not 900V. I think 1kV DC rated caps, or higher, are better for mains RFI filters.

The main problem is they made many X2 caps too compact so the insulation is just too thin for voltage spikes that ride on the mains and the insulation gets damaged by them. Better thicker insulation makes the capacitor bigger. But that is the price to pay for reliability in the application.

So I'm much more confident with a 1kV+ rated MKP or other poly cap as an RFI filter device on mains, than a metalized paper official X2 type whose uF value is constantly falling with time and is waiting to smoke. 1200V rated caps are a very good option for size & value and reliability. As noted on another thread, the 1500V rated tuning capacitors for transistorized line output stages make a far superior mains RF filter cap as they also have a very low ESR and welded internal construction.

Of course, ideally, there is always a fuse between the mains input and the RFI filter so the current is limited if the capacitor shorts outs, but sometimes you will see the RFI filters built into IEC connectors with no fuse and I don't think that is a wonderful idea, but at least they are enclosed in a metal shell that mitigates the fire risk.