As long as the replacement power supply you installed was a good working one, not one that is ancient, and it has the power (watts) to run everything in the slot machine on the 12vdc and 5vdc power then it should be fine. The pc power supplies I've seen had enough wattage, seems like they were around 135 or 150 watts but I know they also made lower wattage ones for small pc's.
Also, when you added that replacement power supply you probably had a lot of wires that were spliced or crimped or twisted together to make the connections. That's where the possibility of a weak or bad connection could be. So you might want to recheck all the wiring connections to see if anything is loose.
If you plan to get another slot machine down the road it won't hurt to get another DBV-200 head now and see if that fixes this machine that is resetting. If that isn't the problem it will still be good to have a spare DBV-200 around. And someone is always looking for one so you could probably sell it fairly easily if you wanted to.