How to connect RS232 ("Opto-RS232")
It looks like the opto-cable is resuing DTR and RTS as it's own power input pins. 

Your MAX3222 uses charge pumps to generate the high positive and negative voltages for signalling over RS-232.



To me, if your cable doesn't draw a lot of current, the easiest thing to do would be to connect the positive supply (DSR) to V+ (pin 3) and the negative supply (RTS) to pin 7 of the MAX3222. Voila, power.

If your cable needs more juice, you'll need to provide it by some other means (a separate power supply or charge pump).