I think I have a bad power supply. How can I check it. I have a tester, but I am not sure how to check leads. Do I check one of the four pin plugs with the leads and which ones do I check? I have a red lead on my tester which is hot and black lead which is ground. I know the red wire on the four pin plug is the hot. Is the black the ground? Is the red 5v or 12v? How about some help.