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

The first one was Tiffany brand. I do not see the brand any more. They also made heavy brass binding posts. The Tiffany cord did not make a huge difference.

About a year later I bought a Black Mamba power cord from Synergistic. That one made an obvious difference. However, the sound was not right in some ways, like off tone and forward, etc.

I traded it in after about 4 months. 

I am satisfied with my contribution to the Thread, especially showing a particular Cable Type using PC Triple C Wire, that has caused quite a positive impression on more that one person.

The Wire in use as a result of my loaning Cables, has also caused one well known producer of Cables in the UK to have as the end result of experiencing PC Triple C, the use of it in a Cable supersede their own Cable designs. 

The Link I put up, clearly shows not too much monies are needed to acquire a length and have the experience for oneself.

Pure Copper Connectors will add to the cost of not already owned. 

I have been inquisitive and like to step around anything that relates to the following.  

  "There is a principle which is a bar against all information, which is proof against all arguments and which can not fail to keep a man in everlasting ignorance-that principle is contempt prior to investigation."

@steakster Excellent examples of experts.  My background is Military electronics so very familiar with the high level of expertise required in various situations.  That world certainly offers lessons applicable to audio. Even in Military applications it is not uncommon to encounter attitudes like - "What's the big deal, it's only wire".  

Unfortunately, the audio hobby suffers too many armchair experts that think knowing how to spell Engineering, Science, or Physics indicates actual knowledge and wisdom.  

@curiousjim 

When I bought my briefly-used Classé Audio SS power amps in the late '80s, the previous owner had already outfitted them with Cardas Quadlink power cables (a lower rung in their hierarchy).  At some point I experimented with using some ordinary AC cable, and heard the difference immediately, and went back to using the Cardas.  I don't recall the specifics, but generally Cardas cables seem to result in more robust bass that is easily noticeable if the system can reproduce it.  My system, with a very fine Classé preamp and Apogee Duetta II ribbon speakers, was/is quite revealing.  But I did not hear a difference when recently replacing the power cables on my Bluesound Node streamer or my Denafrips Ares II DAC with low-end Audioquest power cables. 

So, I guess I'm in the camp that says AC cables make more of a difference with power amps than source components, although I'll admit my sample size is small. 

The original owner of my Classé Audio gear, a dealer, was very enthusiastic about Cardas wire--not only did he replace the power cables with Cardas, but he replaced internal wiring on various products with Cardas wire.

@strawj 

What is your system? The effect of power cords is depend on your system. Very helpful to know where you are coming from. You can see my systems under my ID.