12Vdc 5A Power supply electricity consumption
In general, the input power taken by a power supply will be equal to the power delivered by the supply, plus a little lost/used in the supply itself.

In your case, the supply is capable of delivering 60 watts (12 V x 5 Amp), and when delivering its rated output might draw 65 watts from the AC mains.

If your LEDs only demand 2 Amps, the supply will only be delivering 24 watts, and might draw about 29 watts from the mains.