So, the reset protection board solves one type of power problem on your main power driver board, and it does that well.
I've had very good results with this kind of board, even when I use it inappropriately (as a 'keep the pinball working indefinitely' instead of a 'keep it working until it can be repaired properly').
That having been said, I've also had the experience you are having... the power board needs to be repaired, and the 'no more resets' board showed a DIFFERENT problem immediately.
The fact is that your power driver board is probably twenty three years old, and it probably has multiple failure points that need attention, not just for the +5v (which needs to be rock-solid perfect for no resets), but also the +12V, and the +12V unregulated, the 70V, etc.
I always shrugged my shoulders when I had your experience, and knew that I would have to fix the board properly right now, instead of later.
It's not the daughterboard problem, it's a 23 year old board that has seen heavy use for a lot of it's life that needs a fair amount of the power circuitry properly looked at and repaired.
Sorry you are having problems...
But getting a proper repair for your power driver board was always going to be the better option.
You are just going to have to do that now instead of later.