What was the first power cable that you noticed a difference in the sound?

@curiousjim In your price range the LessLoss Cmark Prime is $485.00 and was a marked improvement over my Zavfino Majestic Mk III cables that are on sale for $450.00. I also prefer the LessLoss as they are flexible. I upgrade to the Classic entropic for my DAC. 

@jacobsdad2000 

Out of curiosity, what is their Entropic process?

Thanks.

The only under $500 power cables that I found a noticeable improvement from are Audio Art Cable power1 Classic, and power1 e Croy. Had tried Signal Cable, PS Audio, and a few others that were no better than the stock equipment cords.

I started with a bunch of DIY Supra Lorad 2.5 SPC and Belden 19364. The differences they made over stock cords were obvious.

The Supra cleaned up the sound and brought more detail. The Belden energized the music and increased bass quantity, though at the expense of increased noise floor. 

I have since upgraded my cords to assortment of brands that cost average $800-1000 each. There is a marked improvement in sound quality in cords priced around that range compared to those below $500. From that price range to mega bucks ones like Ansuz's and Synergistic's higher ends, negligible. I know, I exhaustively home auditioned plenty of branded cords and where not possible, I did AB comparison of cords in showrooms. Without these higher end cords, my setup had substantially smaller soundstage and less slam. Upgrading fuses in both my integrated and DAC brought also significant improvement in clarity; I use Hi-fi Tuning ones.

These are what I have currently in my setup: 

Mains: Nanotec Power Strada 309 (with Furutech FI-50 NCF)
Amp: SoundString Gen 2 SE High Current
DAC: Divini Audio PT-Z 7N
Sub: Real Cable Citrine
Desktop streamer: Nanotec Power Strada 308 (with Furutech FI-50)
Desktop mains: Synergistic Research Foundation High Current