QUOTE(lordvader129 @ Dec 28 2008, 10:12 AM)

a lot of cellphone and laptop chargers are designed fro 110-240v, so if thats the case you adaptor may just allow it to plug in in the US without actually changing the power thats flowing
for the xbox you will need an actual stepup converter to switch the power from 110v to 220v
alternatively you could pick up a new power supply for the xbox (not just the power cord) they have switchable ones that can be switched back to 220v if you return to europe
ETA: also, since the xbox is PAL you will have to switch the video output to NTSC, this can be done easily using enigma videomode switchdisc, available at the usual places
Excellent suggestions lordvader129.
Just to add to the above:
Check this post from another Forum
HERE ,to see if your power supply is the same as shown in the tutorial. It will save you some money if it is the same.
If it is, then do the mod, then use the Enigma Video Switch Disk as instructed by lordvader129.
Good luck! I hope your PSU is the same as in my tute.
Regards,
DarkMatter