This is a question that many people ask themselves when they buy an electric appliance. However, the answer to this question varies depending on the type of appliance. An electric kettle needs very little power to function. It only requires about 0.3 watts and can be plugged into the mains at any time. On the other hand, a microwave oven needs about 200 watts of power to run and must be plugged in for it to function properly.