Where do cables upgrades have the most impact?

Curious if those saying the power cable had the most impact are plugging into a power conditioner or a wall outlet?

Well...after reading everyone’s responses what I surmise is that opinions differ because everyone’s system is different and cable upgrades impact systems differently. So...the old audio adage of you have to try it and see how it sounds to you in your system in your environment holds true with cables as with almost everything else in audio.