FWIW...
Can't recall brand/make, but the fancy, gold, and thick enough to tow a house, power cable has made no difference to my CDP or BDP's sound or TV's pic quality.
A £25 Tacima mains block gave my previous hi-fi setup - an Arcam CD73, A70 and KEF iQ7SE, with Chord Co Carnival Silver Screen Bi-wire - improved separation, tighter bass and an overall 'fuller' concert hall-type sound, although a Tacima did now't for my AV kit. However, with my current hi-fi, see below, the Tacima produced a 'gloopy' sound compared to the MasterPlug mains block's clearer and more open delivery. The MasterPlug cost £7.
Similarly, my current speaker cable produces a more balanced and neutral sound compared to the Chord - and the latter costs twice the former's price.
Kimber Kable Silver Streak (SS) RCAs have generally opened up and released my TT's hitherto moribund top-end range and detail. The SS costs c. £160 for 0.5m. So thank Gawd for eBay; grabbed my SS for £57. (And many thanks to Big Chris for the clue re Kimber SS.
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I guess the moral of the ramble is believe what you hear and only pay what you need to?