Legally, you are required to pay VAT and import duty when buying in the US and importing it, even for personal use.

Chances are, you aren't checked. But if you are, having the original packaging or charger will be noticed by customs. They might even have data to determine country of origin from a serial number, or notice that it's a version that wasn't available when you left for the US etc. And if they ask, the burden of proof is yours to show you bought it in the EU.