Does exactly what you want it to. Of course this is NOT a voltage converter, it merely changes the physical plug from US to UK. As such, the voltage on your American item needs to support the UK 240v. Please ignore the bad reviews of this product, they are from people too stupid to realize this and who plugged an American 115v product into a UK 240v socket, thus blowing fuses. This converter has no 'voltage' of its own.
If your product doesn't support 240v then you need a voltage converter, not just a socket converter.
My Zune charger supports 100v-240v, so this works just fine.