In the U.S., and in fact everywhere in North America, the standard voltage is 110 V (with a frequency of 60 Hz) rather than the 220 volts used in Europe.
European plugs are not compatible with American electrical sockets. In order to plug in your electric appliances, you will need a plug adapter or a converter.
Otherwise, you will not be able to use your electric appliances during your U.S. road trip (phone charger, camera charger, laptop or tablet, etc.).
American electrical socket
In general, an adapter is all you need for non-motorized appliances. Examples include camera chargers, phone chargers, laptops, etc.
A converter is necessary if you intend to use appliances with a motor, such as a hairdryer or an electric razor.
Note that a converter can also be used as an adapter; there is no need to buy both. A converter is more expensive than an adapter.
Where can I buy an adapter or converter?
In Europe: Hardware stores (Monsieur Bricolage, Leroy Merlin, etc.), at the airport and many other locations.
In the U.S.: Best Buy, Home Depot, AAA, Samsonite stores, car rental offices, etc. It is also possible to order them on websites such as Amazon.
We recommend buying your adapter or converter before leaving home. That way you will spend less precious holiday time shopping for one once you get here.