I have a long history with Xenarc monitors and their noise issues. In my experience, it is more important to ensure there is no power or ground difference between the motherboard or the monitor. That is, get the power and ground from the same place, as opposed to (or along with) running a second power supply.
Also in my experience, I have found the power and ground to the motherboard to have a much greater effect on video noise than the monitor's. That is - running a larger gauge wire, and a cleaner, shorter, ground, and grounding the monitor at the same place, is usually the answer.
- since I looked at the power supply you're suggesting, I want to try it too!!!