We get this all the time buying in Britain. Often IT kit comes with two power cables; one for the UK and either one for the US or one for Central Europe so we often have a spare cable we can’t use laid around. You’ve received a unit intended for the UK market.
Unless you’re unlucky and the power cable is soldered to the board, Most IT kit these days comes with a removable mains power cable and a switching power supply which is suitable for US 110v or Europe 230-240v so you can switch the cable with one from an IT shop local to you and plug it in directly with no issues.
In the case of your Xbox, as far as I know the power supply is an auto switching type so should be fine with the US supply but double check the power specifications on the back of the Xbox to confirm. Other connections should be fine too.
