Your sump should be running with an inch or two of water in the bottom. When the power goes out the water level in the sump should rise... maybe to half fill the sump or maybe to fill it 3/4 full. If it overflows the sump then you are running the water level in the sump too high or your sump is too small for the tank.
But the correct answer was stated above. Pull the plug and see what happens!!!!! That is by far the best way to gain an understand of how a sump works!!!!