Sometimes it is very easy to tell but Amazon will ship it to customers anyway. Imagine you are looking for a "85W MagSafe 2 Power Adapter" for a MacBook Pro at Amazon.com. First link after search for "apple power adapter for macbook pro" goes to:

https://www.amazon.com/Apple-MagSafe-Adapter-MacBook-Display...

Now read this review (verified purchase):

https://www.amazon.com/gp/customer-reviews/RNA9AYHGA5JG0/ref...