Travelling in the United States you will meet Types A and B sockets, fed with 120 V at 60 Hz. 120 V instead of 230 V: check the rating plate before you plug in a hair dryer. An adapter does not change voltage. The grid runs at 60 Hz. Chargers do not care; mains-synchronised clocks and simple motors do.
You will find identical sockets in the Bahamas, Costa Rica, Anguilla and Antigua and Barbuda. Travelling further to Saint Lucia, Guadeloupe and Greenland means a different adapter. In North and Central America, 24 of 31 recorded destinations use exactly this combination.
Protective earth
Grounded and ungrounded sockets may occur
Not every socket in the United States is earthed: Type B yes, Type A no. Class I appliances belong in an earthed outlet.
Check the rating plate: 120 V suits “100–240 V” supplies, not single-voltage appliances. The 60 Hz supply matters for motors and mains clocks, not for chargers. Check your own device →
An adapter changes the plug shape only, not voltage or frequency. the United States supplies 120 V at 60 Hz – check the rating plate on your device. How to read a rating plate →
If a socket gets hot, crackles or smells burnt, unplug the device straight away.