These Power Converters are called One-Way Converters: this just means that it can only bring 220-240 Voltage down to 110-120 Voltage. In other words, it's a Step-Down Converter. Most customers moving overseas choose this type of Converter because it allows them to use their American appliances and electronics in foreign countries overseas. These converters run on the foreign 220-240 Voltage, and they give out 110-120 American voltage through their built-in Outlets. This is why American appliances and electronics can be plugged into them and operated overseas.