The standard voltage used in the USA is 120V and the frequency is 60Hz. Therefore, if you are traveling to the USA and bringing electrical appliances, you need to make sure that they are compatible with this voltage. Most voltage converters and transformers come supplied with plug adaptors, so you may not need to buy a separate travel adaptor. However, if your appliance or its power supply are not dual voltage rated, the single voltage appliance will have to be used alongside a voltage transformer or converter to allow the appliance to function properly.