Some folks wholesale change all caps on those boards.
I advise against that. The probability of damaging the board is way too high for most hobbyists.
The only cap that really matters is C5 on the WPC-089 power/driver board, and perhaps, someday, the equivalent cap on the WPC-95 power/driver board.
C2 (leaks) and C4 (can cause resets) are far more important than any other caps on those boards.

preDCS sound boards have 7x 47uf caps that are mostly dried out after all this time. Replacing them can marginally improve preDCS sound.

Testing for AC ripple is a good idea. It allows you to leave the cap in the board to test.
An ESR meter would be better but requires removal of the cap.

Yes, these big caps are used to smooth the various board DC voltages as rectified by the bridges.

Can a cap be absolutely indicted for a reset issue?
That might be tough.
Replacing a cap and then resets vanishing is only circumstantial evidence. PROVING that the cap was the issue would be nearly impossible. You'd have to remove and replace the cap "in-situ", which isn't possible.

I authored part of the discussion linked below. Enjoy.
https://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Game_resets

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Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/Contact ... for board repairs
http://www.PinWiki.com - The Place to go for Pinball Repair Info

I've encountered the "rolling line" display issue on a couple WPC-95 games, as described here:

https://www.pinwiki.com/wiki/index.php?title=Williams_WPC#.22Rolling.22_Horizontal_Line_on_WPC-95_Display

Otherwise, I haven't needed to replace any other significant WPC-95 driver board caps yet. I suspect that might start changing in the next few years as they get older.

For WPC-89 driver boards...I've seen issues all over the map. Sometimes caps are involved, sometimes not.

I usually test removed caps with an Atlas ESR70. If the cap is way off spec, then I figure it's usually a good indicator that it was contributing to a problem.

I'll also test the new caps going in to make sure they aren't duds or counterfeits.

I Recently replaced all 15000 uF caps on a STTNG driver board. Some had slight bulging on the top .that’s a bad sign on very small capacitors in switch mode power supplies, A good way to test for ripple on the lines is with a quality multimeter on AC setting . On this machine ripple was 0.2 on the unregulated 12 v line .all other voltages were 0.04 ac or similar which is acceptable. I prefer to replace all caps and sometimes the bridge rectifiers as I have good soldering equipment and don’t like recalls . 30 year old caps. Actually one of the capacitors was starting to leak electrolyte. Not noticeable until it was removed. The small 100uf cap beside the 12 v regulator always leaks and should be replaced onsight . A small component tester does a reasonable job of testing these large caps and showed they all were reading about 1200 uF and the esr value was high at about 0.3 ohms. Comparing with the new caps which showed just over 1500uf.