Thought I'd share my experiences with DC cables with an LPS on the Qutest.
First though I'll say I agree the above that upstream improvements matter. But let me qualify that by pointing out that the DC cable + LPS or PSU is also part of the upstream gear (if that's the direction referred to as upstream). On the same side of the coin, I'd say say that the quality of BNC or other digital input cable into the DAC makes a difference, as well as the electrical purity in the source component feeding it. I would further speculate that a good enough LPS with an DC cable of decent gauge & insulation has the potential to absorb some of any potential impurities from the digital cable coming into the DAC.
For downstream gear such as RCA cables, amp and headphones - these make an absolute difference because DAC improvements only make a difference if the equipment its' being sent to is up to par. But that's as far as I can agree. Because with a new custom LPS I've got from a confidential source along with a very robust DC cable that I will mention below, I am hearing profound improvements to the sound that are unmistakable and repeatable when A/B'ing both DC cables and the stock wall-wart of the Qutest vs. the custom LPS I'm using. My current downstream gear can be considered mid-fi, not the best but certainly revealing enough to show huuuge differences with clean power to the Qutest using a good DC cable and LPS.
My journey of aftermarket cables with an LPS for the Qutest went like this: Initially I used the provided stock DC cable from the now-closed Ciunas Audio. This yielded a much more smooth, intimate & organic sound with better detail / texture, paired with the LPS I formerly had from them. Next I tried a blue Gotham cable from Ghent Audio. IIRC the resolution & intimacy improved, as well as bass definition, but at the same time the treble became somewhat exasperated causing fatigue. Next up was a 4S6G cable also from Ghent Audio with JSSG360 shielding, which I regard very highly. The bass really came into its' own in a very good, impactful and controlled way, soundstage seems larger, everything is more puristic and all traces of digital glare / harshness in the highs have disappeared. Several A/B comparisons of it to the much thinner stock cable from Ciunas has shown a distinctive and repeatable difference, and especially when comparing the Qutest stock PSU to my custom LPS with custom 4S6G aftermarket cable - the difference was significant enough to make me question whether I'm still listening to the same song - the difference was THAT huge! Hard hitting bass with great definition, smooth silky mids, clean highs, etc., making the Qutest with stock PSU sound low-fi and clinical by comparison.
Of course the quality of said LPS makes all the difference here, the function of the DC cable being just to transfer the purity of its' power as faithfully as possible to your DAC (or 'color' it depending on the materials). Actually both the Gotham and custom 4S6G cables both sounded similar to each other, the former being just a little brighter. I also seemed to notice a somewhat bright leaning sound initially with the custom 4S6G cable, but interestingly with just around 6 hours on it that seems to have subsided, leaving me with what it seems as a more neutral sound, even when comparing the FR to the stock Ciunas cable. I owe @HumanMedia thanks for the formula for this thick black DC cable. Did you also experience the treble relaxing after burn-in, or was that just my imagination? Also I actually don't share your sentiment about any bass roll-off with mine, maybe that depends on the specific LPS pairing.
For those left scratching their head, I'll illustrate it.
The Gotham cable has quad solid copper OFC wires with JSSG360 shielding - which I was told is similar to creating a Faraday cage around the cable to keep out EFI/RMI. Mine looked like this one:
(generic photo)
Ghent Audio recommended the above as well as this as the better type of DC cables.
Neotech UPOCC 7N Copper 18AWG DC cable. This also has JSSG360 shielding, however HumanMedia reported that it's inductance is too high with its' thicker metals instead of star quad which means separated into four wires; resulting in a slow & dull sound.
(generic photo)
The one I was recommended from HumanMedia was the 4S6G cable which is this one, but also with JSSG360 shielding, which I requested on order by email and also specified 2.5mm barrel DC connector on one side and micro USB on the other side. This is also an OFC star quad cable using the best / thickest gauge possible for the micro USB connection type without getting into the territory of excessive inductance. The result looks similar to the exterior of the above cable as you can see below.
(my 0.5 meter Canare 4S6G OFC cable with the JSSG360 shielding and a micro USB connection on one side with 2.5mm DC connection on the other side. In the middle is the supplied stock cable that came with an LPS from the now-closed Ciunas Audio which is acceptable quality of unknown material, and on the left is the stock Qutest DC cable for reference)
Just to avoid confusion, the Gotham cable was found by several to be too bright, the specified Neotech cable was found too dark / dull by another user, and to me the recommended variant of 4S6G cable shown above (right) was the best so far by a good margin. And RE my current LPS, I have to keep the source on it confidential for now.
Also HumanMedia would you mind to mention your source for a Canadian sourced silver DC cable that other users swear by? I'm just curious on the price & appearance at least.
First though I'll say I agree the above that upstream improvements matter. But let me qualify that by pointing out that the DC cable + LPS or PSU is also part of the upstream gear (if that's the direction referred to as upstream). On the same side of the coin, I'd say say that the quality of BNC or other digital input cable into the DAC makes a difference, as well as the electrical purity in the source component feeding it. I would further speculate that a good enough LPS with an DC cable of decent gauge & insulation has the potential to absorb some of any potential impurities from the digital cable coming into the DAC.
For downstream gear such as RCA cables, amp and headphones - these make an absolute difference because DAC improvements only make a difference if the equipment its' being sent to is up to par. But that's as far as I can agree. Because with a new custom LPS I've got from a confidential source along with a very robust DC cable that I will mention below, I am hearing profound improvements to the sound that are unmistakable and repeatable when A/B'ing both DC cables and the stock wall-wart of the Qutest vs. the custom LPS I'm using. My current downstream gear can be considered mid-fi, not the best but certainly revealing enough to show huuuge differences with clean power to the Qutest using a good DC cable and LPS.
My journey of aftermarket cables with an LPS for the Qutest went like this: Initially I used the provided stock DC cable from the now-closed Ciunas Audio. This yielded a much more smooth, intimate & organic sound with better detail / texture, paired with the LPS I formerly had from them. Next I tried a blue Gotham cable from Ghent Audio. IIRC the resolution & intimacy improved, as well as bass definition, but at the same time the treble became somewhat exasperated causing fatigue. Next up was a 4S6G cable also from Ghent Audio with JSSG360 shielding, which I regard very highly. The bass really came into its' own in a very good, impactful and controlled way, soundstage seems larger, everything is more puristic and all traces of digital glare / harshness in the highs have disappeared. Several A/B comparisons of it to the much thinner stock cable from Ciunas has shown a distinctive and repeatable difference, and especially when comparing the Qutest stock PSU to my custom LPS with custom 4S6G aftermarket cable - the difference was significant enough to make me question whether I'm still listening to the same song - the difference was THAT huge! Hard hitting bass with great definition, smooth silky mids, clean highs, etc., making the Qutest with stock PSU sound low-fi and clinical by comparison.
Of course the quality of said LPS makes all the difference here, the function of the DC cable being just to transfer the purity of its' power as faithfully as possible to your DAC (or 'color' it depending on the materials). Actually both the Gotham and custom 4S6G cables both sounded similar to each other, the former being just a little brighter. I also seemed to notice a somewhat bright leaning sound initially with the custom 4S6G cable, but interestingly with just around 6 hours on it that seems to have subsided, leaving me with what it seems as a more neutral sound, even when comparing the FR to the stock Ciunas cable. I owe @HumanMedia thanks for the formula for this thick black DC cable. Did you also experience the treble relaxing after burn-in, or was that just my imagination? Also I actually don't share your sentiment about any bass roll-off with mine, maybe that depends on the specific LPS pairing.
For those left scratching their head, I'll illustrate it.
The Gotham cable has quad solid copper OFC wires with JSSG360 shielding - which I was told is similar to creating a Faraday cage around the cable to keep out EFI/RMI. Mine looked like this one:

(generic photo)
Ghent Audio recommended the above as well as this as the better type of DC cables.
Neotech UPOCC 7N Copper 18AWG DC cable. This also has JSSG360 shielding, however HumanMedia reported that it's inductance is too high with its' thicker metals instead of star quad which means separated into four wires; resulting in a slow & dull sound.

(generic photo)
The one I was recommended from HumanMedia was the 4S6G cable which is this one, but also with JSSG360 shielding, which I requested on order by email and also specified 2.5mm barrel DC connector on one side and micro USB on the other side. This is also an OFC star quad cable using the best / thickest gauge possible for the micro USB connection type without getting into the territory of excessive inductance. The result looks similar to the exterior of the above cable as you can see below.

(my 0.5 meter Canare 4S6G OFC cable with the JSSG360 shielding and a micro USB connection on one side with 2.5mm DC connection on the other side. In the middle is the supplied stock cable that came with an LPS from the now-closed Ciunas Audio which is acceptable quality of unknown material, and on the left is the stock Qutest DC cable for reference)
Just to avoid confusion, the Gotham cable was found by several to be too bright, the specified Neotech cable was found too dark / dull by another user, and to me the recommended variant of 4S6G cable shown above (right) was the best so far by a good margin. And RE my current LPS, I have to keep the source on it confidential for now.
Also HumanMedia would you mind to mention your source for a Canadian sourced silver DC cable that other users swear by? I'm just curious on the price & appearance at least.