When does an electronic fly swatter consume power?
I think there are two main moments of power consumption:

1 - You press the button and the circuit is powered up, providing the metal grids with maybe thousands of Volts.

2 - When you hit a fly: killing a fly MAY be mainly due to power stored in huge capacitors or may be a sum of capacitor energy plus the power supply. Either way, it will have to consume power to charge the capacitors back up.