Your powersupply is not enough, and the line you have is called a hum bar, where the 50/60Hz power gets into the video signal.
First, get a decent enough power supply. Look at old laptops, they often have a 13 volt one. Otherwise try it on the molex on a computer to see how it goes (yellow is 12v, black is ground)
Till you have sorted out the under speced power supply its pointless checking the grounds etc between the jakks and the display.