Hi I have a power supply tester which is a little box you plug the cable in and you plug the power supply into the wall and see the green LED's light up. Below is a photo
On some power supplies the -5V does not light. On some others it does light. Both power supplies are 20 pin power supplies. I remember hearing that some times it is normal for the -5V to light up depending on the power supply, but I just was wondering if that was true or not.