I bought the JitterBug to use with my DragonFly Red and since doing that, I’ve seen that others have filter options (Schiit Wyrd) or use cables with iron chokes. Zeos also has his review on the APC power conditioner, though that’s more for his speaker gear than headphone.
the debate on expensive cables and the recent comment of the one reviewer recommending a $100 AC cable made me wonder more about it.
what do you do?
My electronics are on UPS that outputs a sine wave form. I see no reason to go further to things like $100 power cables.
well, all UPS output a sine wave form…just whether it’s pure or artificial. 
I have a pair of Jitterbugs. They do change the sound. Whether that sound is “better” is very much a personal taste and equipment dependent. I like to use a Jitterbug while listening to DT990 because it reigns the treble in just a bit and sharpens their imaging. But on my M1060 it dulls the treble a bit too much and brings the mids even more forward, making them sound shouty/honky at times.
The equipment must just share a common ground… you can maybe look into glavanic isolation, but if you have to resolve to that you have a serious flaw in your wiring somewhere. Remember USB is a digital signal… there can be no “Noise”.
Some problems also occur if the USB port is incapable of producing enough power. Many max out at 1A 5V and the dragonfly is capable of exceeding that very easily.