If you have the old style OBS, the smoke generator should plug directly into a wall outlet. Mine does.
Not sure how the new version (BS611) smoke generator is wired.
If you're just running the smoke generator, an 18 ga cord will work. But I always like running heavier cord if I can.
Amazon has computer cords, and if you search, you can find heavier gauge versions.
Typical computer CPU power cord plugs are NEMA 515P for plugging into the wall, and IEC320C13 (or simply C13) is the male end that plugs into the back of the computer.
IEC320C14 (or C14) would be the female counterpart to C13.
I ordered 2 of these 14 gauge cords recently for wall to PID, and PID to smoker (OBS and single probe Auber).
http://www.amazon.com/Tripp-Lite-P007-002-Power-5-15P/dp/B0027JPKIE/ref=pd_sim_e_3Hopefully this is clearer than mud.