I have an old Switch Click that says it uses a PS2 connection. This is not the current PS2 connection either. Did the original Apple computers have a PS2 port different from the current PS2 ports on a PC? Is there an adapter for this?
Apple had ADB ports, (Apple Desktop Bus), not sure if you can find an adapter, but some clues...
http://stuffaboutstu.blogspot.com/2005/02/adb-to-ps2-adapter.html
http://filetonic.com/blog/2011/12/28/keyboard-adapters-for-mac-computers/
http://www.geethree.com/adb/index.html
Or do you mean PS2->USB, or maybe ADB->USB?
Tash Switch Click switch -- serial #5001, PS2 #5002, MAC #5003
