your phone can't possibly be drawing more than 2.1 amps?? I don't even think the note2 going balls out draws that much, only tablets
I could be wrong but I'm willing to bet your phone is charging at .5amps because it thinks it's connected to USB, does it say charging AC??? If not then it will die while plugged in.
You're using a samsung phone right? judging by the battery size it's an S2, type this into terminal emulator (root required) while your charger is plugged in, it will tell you your charging rate, I think you have to divide it by 10 to get the mah rating
Code:
cat /sys/class/power_supply/battery/batt_current_adc
EDIT: Or even try this APK, it essentially types that command for you and gives you a notification with your charging rate
[APP] Skyrocket Charger Test - xda-developers