A cap attached across the DC terminals of the solenoid bridge rectifier will give the solenoids more power. There's one on the power supply, but it's just 100uF, which doesn't have much affect on the power. What value is the capacitor that's connected to yours? It should say on it somewhere. If it's higher value, it could be there to make the game play faster, or if it's just ~100uF maybe they didn't feel like doing board work...