Original or licensed accessories, which are generally tested by Nintendo, can be clearly identified by two things that appear on the packaging and/or manual:
The statement "Licensed by (the Trademark of) Nintendo...". Our own products do not feature this.
The golden "Original Nintendo Seal of Quality". This is a circle surrounded by golden points and a white area containing the above sentence written in golden letters. The Nintendo name is shown as our logo. In the lower right corner there is a small "TM".
The quality seal is your assurance that you have bought a Nintendo quality product which works correctly.