Bang on the button. Mains Caps = 50 HZ @ Low Frequency smoothing. Run cool.
Secondary Caps after SMPS on Secondary outputs = High Frequency smoothing. They run hot. Lots of work to do. And dry out/up...etc. Or sometimes just visibly swell up or burst at the top. You can spot them easily if you know what you are looking for.
Main Smoothing Caps also go faulty though.....not through heat but rather things like high Mains voltage (where they visibly pop the top of the can) or simply wear out due to age and/or bad manufacturing. On a CRT TV for example, the first sign of a open MSC is a humbar that moves down the screen. And disturbs the picture. On a 220VAC input on a SMPS, you need to read around 320VDC across the MSC.
No ESR testing or anything....if you have 320VDC...your MSC is working and doing its job.
Not the most Technical explanation in the World....but a good PRACTICAL guide for basic SMPS fault finding regarding Capacitors.
Putting you on proper green
vlad777
Enjoy
Regards,
tvtech