I'm a big believer in power conditioning for many years. I use it on my stereo rig back in the day and still do, and now for the last 2 years on my headphone rig. I had favorable results with an Audioquest Powerquest 3.
For shitz and giggles, I pulled my Sound Application Line Stage conditioner from my stereo rig and popped it in my headphone rig. Wowsers! Improvements in all areas of the sonic spectrum and easily outperforms the AQ PQ3 as it should due to its higher price tag when in production.
Yes, I know its probably an overkill using a Sound Application Line Stage for my modest headphone setup, but since it's just sitting there, I might as well use it for now since I can't listen to my stereo rig due to family constraints.