Tekken Stick works with PS2 USB adapter, but not with a PS2

This is bizarre.

I had a Tekken Stick that worked with PS2’s just fine until the cord got mangled. I bought another cord off of a member here at SRK and now it won’t work with PS2’s anymore. It works fine on my pc and PS3 when I plug it in through the GUN port of my USB adapter, but not through the GAMEPAD port.

Anybody got an idea what’s going on?