New expensive power cord for amp and no change in sound?

           For anyone ACTUALLY interested in doing some study, another rewind:

        Anyone needing a rationale for experimenting with new cables in their system and/or feeling dissuaded by the Church of Denyin'tology's antiquated electrical doctrines: take heart!

        Many new electrical facts have been established in the past 100 years, that support audible differences, between various cables, fuses, etc.

         I couldn't find anything like, "Updated Electrical Theory For Idiots", but- did manage to find something resembling a cartoon, that even a child could follow.  It neither mentions AC/sinusoidal waves in wires, nor does it go into the photon propagation of electromagnetic waves.   It does, however, emphasize/demonstrate how Electrical Theory has progressed, since the 1800s:

              (https://www.youtube.com/watch?v=KGJqykotjog)

        These next two presuppose a certain amount of knowledge, in the field of modern Electrical Theory.    Click, "more" in the first link's third answer, to get its entirety.    Note how it mentions the OLD, "... commonly held misconception that the flow of electricity through a wire resembles a tube filled with ping pong balls...", to which the Denyin'tologists fervently adhere: 

https://www.quora.com/Are-photons-involved-in-all-forms-of-electricity-for-example-when-it-flows-through-wires?utm_medium=organic&utm_source=google_rich_qa&utm_campaign=google_rich_qa

                                            and:

        https://van.physics.illinois.edu/qa/listing.php?id=2348

        It's an established (measured) fact that an electromagnetic wave's propagation and speed, are dependent on the materials, of which the transmission line (cable) are made (ie: Dielectric Constant/permittivity).     The better (lower) the Dielectric Constant the better the flow and the longer it takes for that material to become polarized.     One reason anything that comprises an RLC circuit (ie: capacitors, cables, PC boards), takes time to, "form", or, "break/burn-in".*      

          *Something that makes the Denyin'tologists apoplectic.

   https://resources.pcb.cadence.com/blog/2019-dielectric-constant-of-pcb-substrate-materials-and-signa....

https://unlcms.unl.edu/cas/physics/tsymbal/teaching/EM-914/section5-Guided_Waves.pdf

          Even the most inane (regarding the Sciences) must admit; braiding and twisting wires eliminates/reduces EMI interference.              
          That must lend credence to various cable geometries.

          That better dielectrics enhance the propagation of electromagnetic waves (ie: your music signal), lends the same credence to choosing cables with better materials (ie: Polypropylene, Teflon, air, etc).

           Of course: anything the Church of Denyin'tology's popes can't fathom, they'll summarily dismiss.

         As simple a device as a fuse is: it still carries a sinusoidal signal/voltage, ALWAYS from source to load.

                                                 NOT back and forth!

         Also (as mentioned above): any fuse acts as an RLC circuit, the 'C' of which will be determined by properties of its wave guide's/ conductor's surroundings (ie: glass, air, bee's wax, ceramic, end cap materials, etc).

          Any commonly drawn wire will exhibit a chevron pattern in its crystal lattice, so: why not "directionality" and why OHNO Continuous Cast, single crystal wire sounds better, to so many?

                   Stated above are scientifically tested, measured and proven facts. 

                                  There is no "contest", or "dispute" involved.

         The OP mentions Maxwell, but: obviously they have no understanding of his theory and possible ramifications as regards the above.

          Anyone that feels compelled to harp on not hearing any differences, is obviously too obtuse to understand the term "variables" (as frequently mentioned) and worthy of disregard.

          My only goal in these threads has ever been to encourage those with a mind to experiment with their systems, based on the latest (20th/21st Century's) findings of ACTUAL Physics/science and ignore the Cargo Cult's incessant runway building (objections, convolutions, deflections and obfuscations).

                                                       Happy listening!

Depending on the manufacturer a couple of weeks may not be enough break in time.  For example, my experience with Morrow Audio cables take at least 300 hours to break in.  In my experience power cords can have a significant impact depending on the resolving power of your system. Get yourself a break in file on repeat and give it some time. 

You said “Yes my amp is a stereo Pass 250.8 and the manufacturer said don’t bother”

So, Nelson Pass then properly designed the amp and its power supply. I am not surprised you don’t hear any differences. Why not listen to one of the best engineers?

My First experience with power cords was back in the early 90's Being in the electrical field I was sceptical at the same time open minded because all wire is not created equally. The Store had the exact same system as mine, Amp speakers and CD player. And they swapped out a $350 Nordost Blue haven cord and I could hear a difference in the store. They gave me the power cable to try in my home and I was shocked to hear the difference. I was not really into audiophile if you will, just enjoyed music at that time. the components were in the wrong part of the room and no treatment, due to being married and she had top have the house look a certain way. Blah Blah Blah.

Fast forward To new upgraded audio gear, and the Wireworld dealer gave me 3 power cords to take home. After a week of listening trying all three, I chose the one in the middle at that time it suited the room and the gear I had. This is where my cable obsession took off. As well the room got re-arranged, and the gear found its new home in the room. Room treatment started as well, and then I upgraded all the cables to Silver eclipse 8 and never regretted it for a moment. I found that once you hit a certain price point in Gear, there is a noticeable difference in cables.