When describing voltage for AC, if you say that peak power is 120 V, that only applies to the max. peak of the wave, and not the total watts. If you refer to 120 V peak to peak power, it means that the total voltage from positive to negative is 120. So if you had 200 V peak-peak power, you'd only have 100 V pk power, which would compute to be about 70 watts of electricity.