Iphone se touch id not work while on charging...!

My iPhone SE touch id not work while on charging when i use original apple charger 1a which comes with box. The touch id works well when i use adaptor of 2a local or china during charging. Even its works fine while using charging adaptor of ipad 2.1a. Why is it so, i dont understand? Also is it safe to charge with non-genuine 2a charger?