United States uses 120V, 60Hz with sockets and plugs Type A and Type B.
You may need an adapter while in United States.
Frequency difference is generally not a problem - almost all items (except some types of clocks) will work on both and you shouldn't worry about it.
If there is a voltage difference between countries, you probably won't need a transformer/converter if you use recent devices and appliances because they all work worldwide automatically.
Sockets & plugs category is available in production API version 2.