Maybe this will help, but especially if you want to see something that is measurable rather than perceptible.
These are demonstrations using a ‘dirty mains analyser’ in the
UK and
USA - and the reduction in mains noise by using Shunyata (NR) mains cables.
Such mains analysers are available in the
UK and
USA.
It’s a pity that dealerships don’t have such devices for their customers to borrow - but I suspect their charge for borrowing the device would exceed the cost of buying one for yourself.
Given the price of Shunyata (NR) Cables, paying £/$/€100 for a mains analyser is a small price to pay to establish if such cables would be beneficial or not.
For me, rather than buying such cables specifically for each DSP, maybe buying/using a suitable quality mains block connected to a Shunyata (NR) mains cable is the better option to improve all of my system’s components (not just my DSP’s).