Most of these adaptors work really well. I've based some controllers on them and built other controllers with a flip up lid.
Playstation dualshock to USB, X-box, Gamecube and Dreamcast work really well. Dreamcasts are only tricky cause it doesn't use the L2, R2 and Select buttons. They just go dead. Make sure you get the type of X-box and Dreamcast with the memory card slots.
I built my Stealth stick (examples page) with a Dualshock and included the mode button. My client went nuts on how well it works for him on Xbox etc....
The controls were connected to 1 pin serial female. The pads were hacked into 15 pin male.