whoa, Lik Sang has grown!
They seemed so much smaller when I ordered a Gameboy backup device from them. Great service, they simply mailed me the stuff like a few days after I ordered.
anyways, there are many different adapters, some come with N64 pad connection, some can connect two PSX pads (NO, not that Multitap looking thing, it connects 4 PSX *digital* pad)
Also, as I've said before, a PC controller would come with extra features great for PC games, e.g. the Logitech has a handy throttle. And most brand name controllers would come with software that emulates keyboard, which is handy for "young" emulators that only support keyboard. Lastly, sometimes one PC controller is cheaper than buying a PSX pad + adapter.
To sum it all up, get a PSX pad + adapter if you use it mainly for PSX emulation, and the price is right. If you do a lot of PC gaming OR other emulation as well, you might want to think a few more times.