If they spec 50v you have to use 50v. How much voltage is in that circuit? If it's lamps and under 20 volts you can. Never go down in voltage on a cap if you're not sure what the circuit uses.

The manuals I glanced at don't show this cap, is it on a board? If it is check the board drawing in the manual and it might very well already be a 25v. cap.

From Pinwiki:
"The power supply provides the following voltages:
+20A = 20V DC unregulated (up to 28V at no load); 20V AC comes in through fuse F2, goes through BR2 for rectifying, C5 and C6 are the buffer capacitors (15.000uF). LED2 shows the status of the +20A line."

Capcom runs their unregulated power supplies higher than the other manufacturers.
C5, C6 in +20A suply can see up to 28V with no load. Don't use 25V caps here.
C8 and C9 in the +20B supply has similar voltages so don't use 25V caps for them, either.

You're stuck with pricier caps on Capcom machines.

Yep, I see them on the manual power supply board page now thanks Ed, they spec 35v.

Looking at Airborne schematics - C2, C3 are 1uF, C4 = 470uF.
Which machine?

Quite different.

C1, C2 - 16.4VAC so about 23.2V at cap (plus roughly 10% based on primary voltage and transformer tolerances).
Based on peak voltages, C1 and C2 must be more than 25V rating.
Why 50 instead of 35V? Might have to do with the ripple current rating and peak current. 50V caps can provide bigger 'umph' depending on load.

C3 -- 9.4VAC so about 13.3VDC at cap.
I don't see why a 25VDC or 35VDC cap won't work here.
Might again have to do with current rating.
LT1084 regulator which is 5 amp regulator. I would think a 25 would work here but since I don't know true load, I suggest 35 at smallest.

C4 -- 12.6VAC so about 18VDC at cap.
Since this one can use smaller voltage cap but once again it might have to do with current rating.
At 18V+10% - I would not use a 25V cap here as the voltage margin is getting small.

If it were me - I would stick with 50V caps at all four and not try to second guess the designers.

Still puzzles me as to why they used such large caps on these boards. It would have been more effective and cost less to buy multiple lower capacitance caps and put them in parallel to get the desired value.