Metal prongs on a type-A electrical plug. - JACKREZNOR/Shutterstock Most gadgets and small appliances in U.S. homes have either a Type A or Type B electrical plug, perhaps with a cover to hide cords.

If you've ever looked closely at an electrical plug, you've likely noticed that the ends of the prongs have little holes in them. While this is a leftover design element from early electrical systems, ...

You know the struggle: You go to plug something in, but the orientation's wrong. The prongs are different sizes, so you turn it the other way and try again. Still wrong. You finally get it, third time ...