The P-0921 when purchased comes with a 12V AC 500 mA power supply. What this means is a 12 Volt, Alternating Current, 500 milliamp power supply. Using a higher amperage will not damage the unit, the P-0921 will only draw what it needs as long as it is 12V. The unit comes with an AC power supply, if you are using a 12V DC (direct current) power supply, the system may not function normally. So, in summary using a 12V AC 1.25 Amp power supply (This is 1250 milliamps) is fine. The main thing is to confirm whether your power supply is AC or DC. Power supplies can go bad over time, perhaps the power supply you have now is a replacement. As long as everything is functioning normally there is no reason to change the power supply.