The Online UPS System power is converted from the utilities AC to DC and then back to AC before being sent to the output. When the utility stops, the battery starts to provide to the DC part instead of the rectifier. As the output power is continually produced by the inverter, it's yield waveform is the absolute best of all. So these are reasonable for use by any application that requests superb electrical supply. Because of the consistent twofold change, they are less effective and higher cost because of the extra parts.