The charger is dual 120-240v and can accommodate both. The switch hardware itself is immune, it's merely the charger that deals with the power.I almost considered buying one on Amazon's UK store at normal price, but remembered their electricity is different than the US, lol
Worse case scenario if you don't want to use a UK 3pin to 2 pin USA adapter, would be to simply pick up a cheaper third party or the official Nintendo charger in the USA.