This post regards power cords for electronics (amp, preamp, CD player/DAC), not their use on my Vandersteen 5A Carbons which I've owned for about a year now. As others have said, I am using the stock cords for the speakers, and tend to follow Richard Vandersteen's recommendations for his products.
As far as power cords in general go, I had never had any recognition or knowledge of them, and so had no bias one way or the other before trying them. At dealer recommendation, I first tried them on my amp and preamp (not on CD player/DAC initially). Even my first low priced ones ($300-400 range, Kimber) made a difference that surprised me, actually (I'm trying to use moderate language here) astonished me for cost effectiveness. Then I added a third (a Kimber Ascent) on the CD/DAC and was even more astonished. At the time (and now) I thought it was the best bang-for-the-buck I'd ever done. Then, at dealer recommendation, I upgraded all to Audioquest NRG-1000s at much higher cost. I tender the following tenuously because I did not A/B them and inserted them along with other wire changes, in other words, don't rely on it, but I'm not convinced at this point that this upgrade was commensurate with the cost increase. Maybe I would be if I A/B'd them or added them to the system without any other changes at the time. At any rate, my point is that, having wandered into the power cord landscape with no knowledge and no pre-conceptions, there wasn't any question at all of a big improvement when I started to use them, especially in the area of cost effectiveness. Anyone could have heard it. The Kimber Ascent on the CD player/DAC (Resolution Audio Cantata) in particular was incredibly cost effective, making me think it's a huge bargain. In fact I even wrote the CD player manufacturer, saying if a power cord for a few hundred bucks could double the sonic quality of a six or seven thousand dollar unit, why didn't they incorporate it as OEM since it would add relatively little to the retail price and have a big impact on sonic quality, or at least offer it as an option. Other system components are Theta Dreadnaught I amp (two mono modules), Aesthetix Calypso preamp (not upgraded to Signature), all Audioquest wires (ICs, speaker and power cords).
Jim