When we have obtained a blacker background in our gear it always comes down to two things- noise and intermodulations.
Noise can be hiss but buzz is a noise too. So components and layout have to be carefully considered. Intermodulation is a bit trickier. It can occur if a buzz is latent in your system, but the linearity of the circuitry is paramount- the more linear, the less ability for intermodulations to occur.
So I can see that reducing noise on the AC line can help. But for the most part, most 'high end audio' devices do that are so much junk, excluding DC blockers and actually good power conditioners of which in high end audio the only good one I know of is made by PS Audio. Elgar is a company that was never in high end audio, but they made some of the best power conditioners ever made a long time ago. So Elgar and PS Audio have pretty much set the bar for power conditioning; unfortunately I don't see other high end audio companies stepping up to bat. I'd love to be proven wrong. Anyway, the effects of clean power on audio equipment is easily measured and heard.
Power cords, fuses, special outlets and 20Amp AC wiring won't get you a blacker background but they can help in other ways (of these the fuses are the least bang for the buck) which are also measurable. They contribute to a more stable power supply. This is particularly helpful for circuits that don't employ power supply regulation, such as in power amplifiers. But these things have the biggest effect (most measurable and audible) when the amplifier is making power, when the power supply is most likely to sag.
Vibration control IMO/IME affects tonality, but can also affect distortion. So keeping that down in a turntable or preamplifier can really help, but is more likely to be an effect at higher volume levels so is more likely to affect harshness rather than the background.
In phono preamps, having good high frequency overload margins helps to reduce ticks and pops as well as improving the phono section's stability. So that can affect the background quite a lot if you are playing LPs.
Noise can be hiss but buzz is a noise too. So components and layout have to be carefully considered. Intermodulation is a bit trickier. It can occur if a buzz is latent in your system, but the linearity of the circuitry is paramount- the more linear, the less ability for intermodulations to occur.
So I can see that reducing noise on the AC line can help. But for the most part, most 'high end audio' devices do that are so much junk, excluding DC blockers and actually good power conditioners of which in high end audio the only good one I know of is made by PS Audio. Elgar is a company that was never in high end audio, but they made some of the best power conditioners ever made a long time ago. So Elgar and PS Audio have pretty much set the bar for power conditioning; unfortunately I don't see other high end audio companies stepping up to bat. I'd love to be proven wrong. Anyway, the effects of clean power on audio equipment is easily measured and heard.
Power cords, fuses, special outlets and 20Amp AC wiring won't get you a blacker background but they can help in other ways (of these the fuses are the least bang for the buck) which are also measurable. They contribute to a more stable power supply. This is particularly helpful for circuits that don't employ power supply regulation, such as in power amplifiers. But these things have the biggest effect (most measurable and audible) when the amplifier is making power, when the power supply is most likely to sag.
Vibration control IMO/IME affects tonality, but can also affect distortion. So keeping that down in a turntable or preamplifier can really help, but is more likely to be an effect at higher volume levels so is more likely to affect harshness rather than the background.
In phono preamps, having good high frequency overload margins helps to reduce ticks and pops as well as improving the phono section's stability. So that can affect the background quite a lot if you are playing LPs.