MOV (Metal Oxide Varistors) are critical components required in most power supplies when compliance with surge requirements is a must. The surge withstand voltage will depend on the size of the bulk capacitors (if any present), series components (like inductors for EMI filters) and also to a certain degree on how the layout is made.

To lower system cost, MOVs may be removed in some cases, however it is critical to test these power supplies in the lab. Measure the drain to source voltage during a worst case surge event and verify that the voltage remains below the absolute maximum rating.