The US electric current is 110V to 115V, 60Hz AC. Outlets are made for flat two-prong plugs (which often have a third, rounded prong for grounding). If your appliance is made for another electrical system (eg 220V), you’ll need a step-down converter, which can be bought at hardware stores and drugstores. Most electronic devices (laptops, camera-battery chargers etc) are built for dual-voltage use, however, and will only need a plug adapter.