The power in my neighborhood is horrible. Old infrastructure, power lines still on poles, and overdeveloped in the last 20 years. Voltage swings, especially in the summer (think all the air conditioners), are significant. Momentary drop outs are common and the lines are noisy, very noisy. (As I would find out, distortion was as high as 8% at times.)
I've tried higher end conditioners (Audioquest, Furman), which helped, but not enough. So I bit the bullet and purchased a refurb'd Powerplant P12 from PS Audio last December. All I can say is that the difference was noticable in the first 10 minutes. The best way I can describe it is "relaxed and smoother". Which components were positively affected, I don't know, and honestly, I don't care. But I'm definitely liking the results and am sold on the technology.