Go to Menu > Settings > Battery and look for the Fast cable charging option. If it's not enabled, make sure you tap on the toggle and turn it on. After this, plug in the phone with the original charger and see if Fast Charging is working properly now. If it doesn't, try restarting the phone and plug it in again.
For further assistance, register your concern in Samsung Members Application (Open Samsung Members Application > Get help > Send Feedback > Error report/Ask questions).
