It appears to plug into a Game Boy or Game Boy Color and allow you to play DS or Game Boy Advance Games. Without having a Game Boy or Game Boy Color to try it on I really can't say for sure.
Well let me see, there are no prongs to plug into the wall, It doesn't connect to the Gameboy power plug. However It does have two sockets marked in giant letters GBA and DS, I'm thinking "it not" a power adapter.
Yeah I see that.... Could not find one like yours... most are wireless adaptors that I see, and that probably aren't the same thing. Just trying to figure exactly what this is/does...