I just went through a week of going back and forth testing the Qutest with the OEM wall-wart, an iFi iPower, and a Poweradd battery pack.
I did not notice any difference whatsoever between the OEM wall-wart and the iFi iPower. I was skeptical of the iPower going in because I don't like the idea of counteracting noise by adding even more noise, but I figure for $50 it's worth a shot.
Now for the battery pack, I'd be hard pressed to say that I can really hear much of a difference either, especially since quick A/Bin'g of PS's is not possible. I do hear a tiny bit smoother roll-off in the higher frequencies, less of a hiss/scratchiness but extremely mild, and only on certain tracks. If I'm not specifically listening for that I wouldn't notice it. I can't really point to any other differences or improvements.
I am going to end up keeping the Poweradd battery pack now that I know the difference is there, no matter how unnoticeable it may be. And also it's a good accessory to have in general for other things. The Poweradd for the price is the largest capacity battery pack I found that has an easy to read display screen, can output 20v DC (16v to power my Auralic Mini), and has a micro-usb-b for the Qutest.
For reference my setup is: Auralic Mini -> Qutest -> Violectric v280 -> HE1000v2