Manhattan Skyline, NYC
American mains electricity runs on a different voltage to the UK and Europe. America uses 110v for mains electricity which is much lower than the 240v used in the UK. What this essentially means is that the vast majority of small appliances (hairdryers, straighteners etc.) won’t work in the US unless they are dual voltage and you have turned them to 110v. Mobile phones, tablets and laptops are usually OK as the chargers tend to be universal voltage.
The voltage difference also means that you need to be careful when buying electrical items in the US. Check anything you buy can run on 240v. Otherwise, if you plug a 110v item into a 240v socket it will blow up!
US plug sockets are thin 2 pin sockets so you will need to carry converters with you, they are different to the EU ones!
Similarly if you do buy a 240v rated electrical item in the US you will need to buy a UK to UK converter or change the plug on your return.
On the subject of voltage differences, I have managed to blow up two travel hairdryers by forgetting to switch them back from 110v to 240v after I have come back from a US trip. You would think once would have been enough to teach me but sadly not. To save you making the same mistake, always change any dual voltage items back to 240v before you put them away…..