From what i know, the power voltage in USA is 110 while in Paris and most of Europe it is 230-240 volts. All you have to do is bring with you adaptors or transformers that are suitable for your appliances. And it will be a good idea bring with you appliances which operates at 110 to 240 volts. So before travelling make sure that you check the voltage preference of most of your appliances.
I thought there was also a difference in frequency: US = 60hz, Europe = 50hz. Not sure this will matter for most appliances. I'd be more careful with a laptop computer though.... Does anyone have any experience traveling with a US laptop pc??