assuming you have two 12V power supplies you would connect the two supplies in series(the (+) terminal of one supply to the (-) terminal of the other supply). the junction between the two supplies becomes the center ground, the open (-) terminal is the negative rail, and the open (+) terminal is the positive rail, and you don't need so many banana jumpers, and ignore the green ones for now.
once you have it connected that way, you should have 24V between the open (-) and (+) terminals, and 12V between either of the open terminals and the center connection