There are two key differences between the US and here:
- different electrical supply (110-120V, 60 Hz as opposed to 220-240V, 50 Hz)
- different plugs
Most stuff that your're likely to bring, such as phone charger, notebook PC etc. will work on both supplies, and just need a plug adapter, but always check the supply (it'll say on it somewhere the kind of supply it'll work with). A plug adapter is a simple physical device that adapts one style of plug to another: a few Euro at most to buy (but do it here before you go!).
Anything that doesn't work with a 110-120V supply probably isn't worth the hasstle of bringing: just use a local one (e.g. he hotel's hair dryer). You can get adapters (some form of transformer) to convert the supplies, but they're expensive enough and can be bulky (typically depending on the power rating).