Ah that might have been the difference (the USB cable)...
And yes, there's a difference. Every charger, AC or DC, has a rated output it will deliver. You can pick up a generic charger for about $3, but it will be very, very slow to charge your N7 -- if it charges at all. Think of it like a fireman having to choose between using a firehose or a garden hose to put out a fire... Get the one that delivers the current.
Weird, my Scosche reVOLT 2-port USB charger (both are 2.1A) doesn't work... neither with the stock N7 USB cable nor any other one.
reVOLT h2 - 2 Port USB Wall Charger (10 Watts Per Port)
Oh wow I didn't know that. Interesting.. and also disappointing! Going to shoot an e-mail to Scosche to see if they have any response about that.The device communicates itself as a media player. It needs to communicate and negotiate voltage. Some chargers fail that.