power cord affects on video?

One can't argue with what one sees. That's one blessing that detractors have no influence on. With my old Samsung Plasma TV, I tried a Zu Mission PC that I had laying around and the black levels went deeper with more gradations and subtlety in the details. You could make out more image detail in the darkest of settings. 

PLUGE levels (greyscale) were much easier to discern and moire patterns were lessened a bit as well. 

All colors took on more saturation and intensity, contrast was more apparent and brightness levels increased some. It was like the TV was starving for more power.

All the best,
Nonoise

Don't know about TV sets but I put $13 14 gauge shielded power cord on the computer and couldn't believe my eyes - everything looked so much better on the monitor. Sound from the computer was also better. Then I put second power cord on the monitor - no difference. Then I compared $150 audiophile power cord and that $13 power cord - no difference, but my computer monitor is probably 15 years old. More than enough for me, though.

Based on my experience, a good quality power cord would definitely improve image quality. Be aware, what sort of AC plug is used.

Rhodium or Silver AC plugs (with better emphasis on high frequency!) will surly enhance the details, resolution, 3D effect in term of layers of scenes in image as well as vividness, sharpness of edges in scenes. Sometimes it becomes weird  (!!) where in movies when they use those green screen to project other background!!, with layering of scenes you could easily observe that filming has been done in a studio!?

This is because, all these mentioned terms rely on high frequencies of video signal. Low frequency of video consist of definition of contours. 

You don't need to spend too much money on these PCs. You could make your own DIY power cord (~$80, like Neotech PC Hybrid mkIII) with cheap AC plugs like Sonarquest Rhodium or Silver (~$25).

hope that would help...

How do you know it’s the law of diminishing returns? Hint: You don’t. In audio the only constraints are the ones in your head. I suspect yours is a case of penny wise, pound foolish. No offense.