Can I repair my power supply to my 4 slot?

Sounds like something is wrong with the fan as it makes a lound buzzing sound when the unit is on. I notice full replacements are 50 bucks.

Maybe try some compressed air and blow it out a bit. If it persists, you could open and inspect for obstructions.

Another problem I am having with the machine is after an hour or two of play the screen gets white specs that come and go quickly. Not sure what is causing that.

If your 4 slot is in a cab then I reccomend getting a Wei-Ya arcade power supply. They're cheap (20-30 dollars) and supply more than enough current to support 6 slots, hyper 64 etc. Other than that you could try getting a run of the mill 12v/5v PSU from your local electronics store, might be cheaper than the Wei-Ya. A new fan is an easy replacement if the PSU is fine.