I installed a new AudioQuest Dragon Source power cord from my Lumin X1 to my Niagara 7000. The power cord from the wall to the Niagara 7000 is also a Dragon but the High Current version. I bought that cord used.
So, when I first started using the new power cord everything sounded great. However, after a couple of days I started hearing a strident sound. Especially in the upper mid/ treble region. The bass was also constricted. I started blaming the sound change on another piece of equipment that was installed concurrently.
Now, I was under the impression that the Dragon power cord with its DBS system required no break in. But I did inquire about it to AudioQuest who responded that it would still need about 150 hours to break in. It's been close to that now and sure enough yesterday I started hearing the glorious sound that I heard from day one with the power cord only perhaps better.
I must say the difference during break in and now is quite remarkable, I don't remember any other power cord going through this amount of dramatic change.