This is a very simple solution for providing power to a breadboard. A few quick solder connections, maybe some drilling, and a little bit of heat shrink and your ready to go!

Step 1: Parts List

Metal Clip (either with or without suction cup)
heat shrink
header pins
red and black wire
Panel mount power jack
wall wort with plug that matches your power jack, one with adjustable voltage like the one pictured would be best

Step 2: Assemble the Parts

Step one: Solder wires to power jack, solder red to positive and black to the negative contact (this is determined by your wall wort, see diagram)

Step two: Break off two pins from the breakaway header and separate the two pins, making two single pins. Cut two pieces of heat shrink tubing and thread one over each of the wires. Solder a pin to each of the wires, since the pins usually have a plastic ring on them, put the opposite end of the pin in an alligator clip to absorb the excess heat so that the plastic doesn't just melt off. Be mindful not to overheat the pin and melt the plastic ring.

Step three: Thread the wires through the hole in the metal clip. It may be necessary to make the hole in the clip larger to accommodate the power jack, it may also be necessary to bend the clip outward in order for the power plug to clear the other side of the clasp. It can be placed in either direction but placing the plug so that it faces up and fully exposed lessens the likelihood that you might accidentally short the contacts. Add the washer and nut and tighten securely.

Step 3: Usage

If it isn't obvious enough, clamp the clip to the end of your breadboard plug in your wall wort, and push the positive & negative pins into the corresponding rails on the breadboard. If you used the suction cup variety and your work surface is smooth you can affix you breadboard via suction and lessen the chance of accidentally catching the power cord and pulling your whole project off your workstation.