I've never heard of anything like this.. like, why does he go and buy a different version of what you buy him? 
I mean, for starters, stop getting him things. 
This is too weird, and if I were you I'd just directly ask him why he does this until he gives you a straight answer and you need to tell him that it hurts your feelings.

Not saying this is the case, but I had an ex that didn't accept gifts well and it was for a few reasons, like narcissism and pride (he didn't want "charity" or to feel like he "owed me" something) but ultimately because they made him feel guilty since he was cheating, etc. 
Again, not saying your SO is guilty of any of that, but it seems like a red flag. It's definitely not normal at all..

Like even if he's just extremely picky and likes to choose his own stuff, he should let you know like an adult that there was something about the gift that wasn't ideal, and ask if it would be possible to exchange it and shop for the replacement with you. Like, he's not only wasting your money, but he's not communicating what his problem is  which is awful to you, and a real problem.