can i use my ds charger for my wii u gamepad? Like the ds charger can charge the 3ds
No, the chargers for Nintendo handhelds have different variations. The original DS charger is only compatible with the original DS (phat) and GameBoy Advance SP. The DS Lite charger is only compatible with the DS Lite. The DSi charger is compatible with the DSi, 3DS, 3DS XL and 2DS. The Wii U Gamepad charger is only compatible with its namesake. It can't be used to charge other devices due to it being slightly bigger than the 3DS family and DSi charger.
Nintendo Wii U Gamepad Charger