So, I have one of these inexpensive devices, perhaps the very same one, but it does show up for me.
lsusb (for only serial/USB adapter)
Bus 002 Device 003: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial Port
dmesg | grep tty (for only serial/USB adapter)
[12591.384983] usb 2-1.7: pl2303 converter now attached to ttyUSB0
Perhaps it is an adapter gone bad? Or, perhaps it is a kernel version issue? I have updated to kernel 2.6.38-rc4, though I doubt you need one like that to use the adapter. On this computer I am still using openSUSE 11.2 as well. Tell us about your openSUSE setup.