The second characteristic is that MOV's cannot sustain surges that contain a large amount of electrical energy, such as those produced by a lightening strike on the power line. Finally, a MOV is wired in parallel to the computing gear. Thus, it is not uncommon when surges such as a lightening strike are present on the power line that the MOV and the gear it is protecting can both be burned out at the same time. Then, every year or so simply throw away the suppressor and buy a new one. If you buy a stand-alone suppressor, make sure also to purchase a telephone line surge suppressor if a modem is used on the computer.
Conditioners are generally a large, heavy box that contains an isolation transformer.
Conditioners protect very well against surges, because the very short duration of most surges is not sufficient to transmit appreciable power across the transformer. However, conditioners do not store power, and when power is lost the device connected to them loses power as well. Conditioners will last practically forever, as long as they're not overloaded, and give far greater power disturbance protection. UPSs contain an input power supply, an output power supply called an Inverter, and batteries. Standby supplies normally connect incoming line power to the computer, and use their input power circuit to keep the battery charged.