Such a MCU, supply current should be much right?

I designed an electric fan control panel (above the experiment board of its electric current is 200 ma, after become 75 ma), with the full board is normal working current 80 ma, working voltage is 5 v, I prepared a transformer 3 w 6 v, its output current is 500 ma, but the shape is a little big, I'm going to change a small transformer, can provide a 5 v, 300 ma currents can be?

If I provide a 5 v, 500 ma, what is the effect of power source to the circuit?