Abstract: A voltage adaptor outputs 208-220 volts at an outlet and receives two 110 volt inputs. The adaptor has first and second male input connectors that can mate with respective power connectors and a control circuit interconnecting the male connectors to the outlet of the adaptor. The control circuit prevents energizing the outlet unless both male connectors are mated with respective energized power connectors and the phases of the voltages carried by the power connectors are different from each other. Furthermore, the control circuit prevents the energization of one of the male connectors, when it is not mated with a power connector, from the other male connector when the other connector happens to be mated with an energized power connector, thereby preventing a shock hazard that could otherwise arise when one of the male connectors is plugged in but the other male connector remains exposed to the touch.