Adapters do not change the voltage, but they do maintain the ground from the electrical outlet to your appliance. Adapter plugs are needed because electrical wall outlets around the world differ in shape and size. For example, your North American ( USA ) grounded appliances have three blades on its voltage plug - two flat blades and one round grounding pin. All the Grounded Adapter Plugs are listed with the home country first and the country you are traveling to listed second. USA to Europe means that you want to take a North American appliance and adapt the grounded plug for use in Continental Europe.