Completlly stop working after wrong polarity lead been plugged In

one of the first things that go are is the protection diode coming off the + input. Then a fuse and so on. Surface mount fuses are light in color (usially green with white text). Attempt to bypass these components with a small wire or paperclip. Once you follow the lead from positive input you will run into a black rectangular block about the size of a grain of rice with 3 leads. That will be your voltage regulator. Its set at the correct voltage, and since you already have a power supply with a set voltage, then you dont need it. Its also the first thing that blows when you switch polaritys. (voltage regulators have 3 pins - input output and ground) when you switch polaritys that ground becomes the "input" and ..... go to all http://www.alldatasheet.com/ and type in the text you see on that component. It will then identify the component and list its voltage output and at which pin.  Apply set voltage to lead and ... pray? 

Best of luck.