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

My audio engineer feels that it was a current spike that shorted one of my tubes, and so after 55 years I finally caved in and bought a Furman power conditioner from Crutchfield, on sale from $1000 down to $599.

It provides a “current reservoir” of an extra 45 amps for the amplifiers and that has made a big difference with regard to the texture, detail and authority at the bass end.

So that seems a worthwhile investment.

I still use chain-link fence for my cable interconnects.

Grover Huffman Pharoah power cable

Shunyata Taipen around 2010 ,  A small increase in bass, but in every setup  I've used in in , lots of air in highs. Sounds a little unnatural after a little while. 

Nordost Blue Heaven.  When I connected them in, much blacker background.  That showed me power cords make a difference. As my system has changed so have the cables.  I am now running full loom of Kubala Sosna Emotion.  Best move I ever made.