Mains power and conditioning

[Confused]

I did go to a dealer event once. The system they used was basically one I had auditioned previously, with a Devialet 240 doing amplifier duties. However, they had gone "all in" for the event, adding very expensive mains cables (so large that the Dev's rear cover needed to removed), 5k's worth of Chord Sarum speaker cables, plus a mains conditioner. I'd gone along to see what difference all this good stuff would make. (although I could think of better ways to spend 5k than on cables) The strange thing was that I though it actually sounded significantly worse than I had heard previously, with standard mains cables and speaker cables at maybe about a fifth of the price of the Sarum's. The dealer suggested that this might be something to do with the mains conditioner, in some way holding back the amplifier. From what I know, this makes sense. People have different views regarding cables, but to think something like Sarum cables would make things worse seams absurd to me. But could a mains conditioner, perhaps of an inappropriate design for what the component connected to it demands, make things worse? Quite possible I would have thought.