I tested my new cheap Generic 300w PSU using a multimeter
Everything seems fine and have correct and proper voltage except the one wire. The Blue one. It supposed to have a reading of -12v but my multimeter only reads -10.47
I test my PSU by jumping the green and black wire using paper clip.
-12V - This rail is pretty much obsolete now and is only kept on to provide backward compatibility with older hardware. Some older types of serial port circuits required both -12V and +12V voltages, but since almost no one except industrial users use serial ports anymore you as a typical home user can pretty much disregard this rail.