History of domestic electricity
There is no standard mains voltage throughout the world and also the frequency, i.e. the number of times the current changes direction per second, is not everywhere the same. Moreover, electrical plugs and sockets are also different in many countries. Those seemingly unimportant differences, however, have some unpleasant consequences. Most appliances bought overseas simply cannot be connected to the wall outlets at home. There are only two ways to solve this problem: you just cut off the original plug top and replace it with the one that is standard in your country, or you buy an unhandy and ugly adapter.