This is my current ATX power supply that I have:

I am not very happy with it. The picture quality that I get is grainy and the colors are watched out. I know it's not supposed to look that way because the games that I play on my consoles are razor crisp. I am using an Sony BVM monitor by the way. Is the picture this way because of the amp difference? You can see that it supplies +5v/32A whereas an arcade power supply is +5/15A.
More recently I have an audio issue. It involves a MK2 board that I got recently but I do not get any audio other than a static noise. Going to the diagnostic screen, the results show that sound board is working properly. Again looking at the ATX power supply, it supplies -5v/0.5A which is less than that in an arcade power supply which is -5/1A.
Here are images of the MK board and soundboard. The seller has confirmed that hookup is correct and also the sound is working when he had it:


Also, the red LED on the soundboard is on, so it means it's getting power.
Lastly, I get the error "CMOS invalid, Factory Settings Restored, Using CMOS Coinage" after the room check at the start (MK2)
I have already purchased an actual arcade power supply and will hook it up to the supergun when I get it a few days. I just wanted to share this and have everyone's input on this.
Can anyone relate to this? Am I using the wrong ATX power supply for my supergun, are power settings wrong. What is your take on this. Thanks in advance.
Update
Thanks to all your answers, I now know the cause of most of the issues:
The problem regarding the grainy and discoloration in the image is gone. The solution is simply not to connect the PSU and the monitor at the same power source.
The solution to the CMOS invalid error should be fixed by replacing the watch battery on the MK2 PCB.
I found out that the ATX that I am using is not providing any -5v to the supergun. This is most likely the problem. I will provide update when I hook up my new arcade power supply That I will be getting soon and it has -5v.
I changed the lithium battery and the CMOS issue is fixed. All issues in this topic have been resolved. Thanks everyone for your help.