I was just wondering if the ARDSi would work with a 3DS just for backup up/restoring a Pokemon Platinum save (for some reason that's the only game card my USB adapter doesn't recognize)
I'm sorry to say that the Action Replay DSi does not work on the 3DS. Only thing I can suggest is wiggling the cartridge in the USB adapter (forward, backward, left, right, up, down, even diagonally) until it is recognised.
The game still doesn't work with my adapter (I'm being cautious with how long I have the adapter plugged in and inactive after my previous one literally melted), but I was able to borrow a DS Lite to do it.
I have a 3DS AR, but it lacks a MicroSD slot.
The Action Replay DSi I have has a MicroSD card slot for dumping/backing up saves (doesn't work with HG/SS and newer games); the one that works with the 3DS doesn't have the card slot.
Well, there's no such thing as a "3DS AR" as far as I know.
If you really want, buy this
Is your 3ds action replay the same as this one:
Yup, that's the one I got.
On further research, the Platinum cart I've been using may be a fake (I asked on the hkems forums why the card wasn't detected and was told that may be the reason). A second copy (purchased at Gamestop) was detected and dumped/restored the save fine.