Radio Shack brand PSX adapter(A1)
Generic, unknown brand PSX-to-multi adapter(A2)
Dual Shock type PS1 controller(C1)
Nuby Street Fighter fighting game PS2 controller(C2)
C1 AND C2 will work with A1 with no problems on my PC, assuming the adapter's drivers are installed(they are). I can swap them just fine.
C1 AND C2 both worked fine with A2 on my Windows XP computer(which I no longer have).
Neither C1 nor C2 will work with A2 on my Windows 7 PC. I've tried with and without A1 plugged in.
C1 will work with A2 on my Gamecube just fine. C2 does not, I don't know why aside from some hardware incompatibility.