For a system using a single GeForce GT 620 graphics card NVIDIA specifies a minimum of a 300 Watt or greater power supply that has a maximum combined +12 Volt continuous current rating of 18 Amps or greater.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the most critical factor.
The HP OEM 240 Watt power supply meets or exceeds the maximum combined +12 Volt continuous current rating required for a system using a single GeForce GT 620 graphics card.
+12.1Vmain === 14A
+12.1Vcpu === 12A
+12Vsb === 1.3A
-12V === 0.15A
It's definitely not a standard ATX12V design since there's no +3.3V, +5V and +5Vsb rails.