it's not just the wattage you have to consider, but the incoming and outgoing voltages on both the transformer and the item you're powering.
Ideally, the transformer is used to converting an incoming line voltage to the same voltage as the object you're powering. In a lot of cases, it's to drop the voltage from 120v to 12V or 24v. For some items it may even be less - like the power cord for your cell phone has an integral 120v-5v transformer.
A European transformer should do the same thing - except it's converting from a different line voltage (IIRC 220-240v). Using it on a different line voltage can cause either the transformer or the powered item to blow a circuit.
Check your transformer, it should be stickered somewhere to show what voltage and hz it's made for. For use in the US, it should be 110-120v, 60 hz.
at 7:28 PM on Sep. 10, 2009