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

The first power cable that noticed a difference in the sound was a Monsrter PowerLine 300. It made everything sound more open, yet detailed and was a real wow from the standard cable.  The same effect was noticed on inexpensive hybrid through All tube McIntosh systems.  Since that time I have used Nordost Blue Heaven and LessLoss. All were different and more revealing.  I felt dollar for dollar the LessLoss was a better performer for anything under $2,500.

pindac,

I just wanted to give you a little update I talked to the person that is distributing acoustic revive and I also read up on triple C, it is no better or worse than OCC single crystal copper all they've done is come at it from a different production angle to produce longer crystals but they do not say anywhere that their crystals are 125 m long like OCC single crystal is so from what I've been reading and researching triple C is not better than OCC single crystal and now Neotech has rectangular OCC single crystal which is even better than the round and Joe who distributes acoustic revive said to me he can see how the rectangular would be even better than the round OCC or the triple C.

Triode Wire Labs was my first power cord to offer an improvement in sound quality

Nordost Blue Heaven on my Sony surround receiver. I was able to try it for free. I came back a week later and gave the store the money. It transformed my system which I used for music and video. I still own those cables. Blue Heaven is 16 gauge so I would recommend the Red Dawn for it now. I use a Puritan Classic Plus on my Marantz surround processor and a Straightwire Pro Thunder on my NAD M 25- 7 channel amp. I have a separate 2 ch setup that has nice power cables. Probably the first cable you should upgrade even before you start auditioning speaker cables. 

The first power cord that I ever made I thought made a bigger difference than an Acrotec 6 nines power cord that I thought didn't make much difference.  Based on the pseudoscience (voodoo) of the time, It's braided of 18 gauge stranded wires. I don't remember how many but it was fairly thick.  The entire thing was wrapped with strips of bike inner tubes to keep it tight, with the entire thing wrapped with that thick magnetic tape, the kind used in shops, and work areas to hold tools in place with heat shrink on top of that and a blue braided cover and decent plugs.  All truly done with nothing special materials.  The idea of the magnetic tape at the time was to scatter or lessen outside electrical interference but I guess the braiding process takes care of that and I might have reintroduced noise with the magnetic tape.  

   Honestly, I never paid much attention to stuff (power cords) like that at the time but years later I loaned it to a friend to get his take on them. A month later I went to pick them up and I was their a few hours listening to his system with the power cord attached to his amplifier.  As I was leaving he had the standard cord reattached and was playing a live Tony Williams quintet recording  I just heard and his drum kit just collapsed to the left speaker.  We put the homemade cable back in and within a few minutes back to listening, the soundstage changed most notably Tony's drum kit was spread from the left speaker to the center-left of the stage.  Neither of us could figure out why that would happen but it was repeatable.  This was really one of the first times I noticed such a big change with cables and a power cord at that.  Since that time I paid much more attention to powering my system.