It's just a micro-USB -- tell them they have to give you a new one
I don't know if it is a different power profile than, say, my Motorola Droid, though. (My Kindle was the same and I could use my car charger for either). But they could open it up, plug it in, and see if it is charging...
And how do they have it on display if they don't have the power adapter?
They are Best Buy. Keep asking until someone figures it out
Lisa