The Switch v1, not the v2 OLED. The 3DS had their own memory card “format”
The 3DS family of devices used standard SD and micro SD cards.
The games, not the expansion. You could throw any microsd card into your 3DS to get more storage. I’m talking about the memory card the games are written on.
I was thinking more like the power adapter. Game Boy always seemed to have a proprietary adapter.