I can also vouch that the Power Plug is compatible with the Retrolink dual controller port SNES->USB adapter (with Cirka replica SNES pad). I couldn't achieve the Power Plug's maximum autofire/turbo rate on my MayFlash single SNES->PC adapter (it had to be halved) and the Gtron adapter didn't even map the d-pay buttons to the correct keys.

I tested out both the World Class test cartridge and Street Fighter II Turbo (using Blanka's electric shock move) with the Power Plug's autofire in Higan v094.08 accuracy build. Work's just as it did on my original SNES.