[punish3r]

I know I got into this one kind of late, but for anyone else reading this, I just wanted to clarify about the "switch the leads = negative PS"
The easiest way to understand why this wouldn't work is to imagine what a +12VDC PS looks like when piped through an oscilloscope. Properly connected, you'll have a horizontal line 12V "above" the 0V centerline. By switching the leads, all you're doing in reversing the hole and electron flow, thereby creating a "ground" that equals +12VDC, with a VCC of 0V, thereby pumping your energy "backwards" through whatever circuit you're powering, in most cases destroying it. (A side note: manufacturers of battery powered components have known for years that people are notrious for putting batteries in backwards, and therefore install a diode to prevent reverse flow)
Anyway, back to our oscilloscope model. A real -12VDC supply (properly connected) will show a horizontal line 12V "below" the 0V centerline.