It's an official "iPod USB Power Adaptor".
http://store.apple.com/uk/product/MB...mco=MjE0ODcyNw
I
think the UK plug part is just basically a UK plug, while the other part (with a connector for the plug on one side & a USB port for the iPod/iPhone's dock>USB cable on the other side) is I assume the actual AC adaptor.
Apple sell a collection of plugs to fit the unit that has the USB port on it.
http://store.apple.com/uk/product/M8...mco=MTIxODk3Mw
Bit pricey though when all I want is a US plug.
Although, thinking about it, Mrs D has a 3rd party iPod charger with dock connector at one end & 100-240V 50-60Hz AC adaptor UK plug at the other end - I'd guess it would definitely be OK to stick a US travel plug on the plug end of that.