No, that cap won't hold a voltage, it will drop to zero immediately at power off. It's a filter cap for the solenoid voltage.

If you are having resets PinbalManiac is right, usually that's the 5VDC rail. This cap looks to be original, and is likely your culprit. Again, measure with a DMM at the 5VDC test point for 4.75-5.25 VDC. A/C ripple will usually be high if the filter cap has failed.

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Best place to check is at the MPU +5VDC test point. I'm all honesty, the fluctuations are probably the connector pins. Any slight vibration, oxidation or loose fit if you no longer have a gas right connection will cause the MPU to reset. If you haven't repinned the connetors, at minimum repin the psu output connector for the MPU logic power and the input power connector at the top of the MPU. That solved resets on my Pinbot.

I measure 4.91VDC on mine, and the minimum is technically 4.75. Your voltage should be ok, but you are probably losing current (amperage). Have you tried wiggling the connectors with the game running to attempt to induce a reset? Changing that cap on the PSU will likely fix otherwise.