Not all games are encrypted by cart... The most notable one that isn't is OOT
But you're working with a game with per cart encryption (Pokemon X) so normally you would need the original cart...
But the Gen 6 Pokemon games are exceptions. I am highly uneducated on how, but there's a way to decrypt Gen 6 Pokemon saves to be loaded in PKHeX. Instructions are on Project Pokemon iirc. If you were to decrypt the save and load it in PKHeX, you could export it as main, which would let you use the save after patching the secure value
EDIT; I should mention that the saves CAN NOT be re-encrypted
Talking strictly about XYORAS here,
Okay, to decrypt Powersave save for Pokemon, you will need your original cart to decrypt, in order to obtain save1keystream.bin,
so unless you already have that, you won't be able to decrypt a Powersaves save without it.
(to get the keystream, need original cart, do a few things such as restart save and set a code to it etc)
While it is normally impossible to decrypt a save without the cart,
Powersaves save actually backup the private header of the cart (edit: it actually doesn't. you'll need a RAM check of the powersaves tool while the cart is inserted).
(and btw, Powersaves doesn't encrypt the save. The save is encrypted by the 3DS using the header, and powersaves simply dump it raw + header
)
Meaning if you:
1. Inject the private header into a Rom (
http://gbatemp.net/threads/tutorial...o-cia-plus-extracting-private-headers.432600/),
2. Inject the encrypted save (minus Powersaves' own header from the save) into the ROM
3. Place rom on red cart on Gateway3DS
It should run, as you are basically emulating the cartridge.
edit:
I'm not entirely correct, it seems.
Powersaves saves don't dump your header (they dump something else while writing a header into your save)
So your only issue, is finding your private header.