How long have you left it on the charger? I've had mine come back overnight. Or even a full day.
It's not that there's a problem with your charger, it's that the Touchpad's charger delivers a different level of charge from most other cables/bricks. If the TP's battery level falls below a certain level, it gets tough to get a charge to it, and usually only the stock charger or touchstone work. A lot of people have had this issue, so searching for them would probably give more info about it than me.