s in North America
are different from those found in Europe. The North American model has two flat rectangular prongs, each with a hole near the tip.
Within the outlet, there are 2 plates with dull indentations that press into the holes and help hold in the cord, so it doesn't fall out as easily.
Also, some special outlets allow you to lock the cord into the socket, so it can't be removed, by putting rods through the holes. A few bars and pubs have it, so you can't unplug the vending machine.
Ask any hardware store employee.