Can a better power cable make a difference if NOT plugged directly into an outlet?

I would have to say yes it might. As @erik_squires mentioned, a serious well shielded cord can make a difference wherever. At least it had for me. Tried one on my amp directly into the wall to replace the standard cord ( into a decent Hubble 20amp receptacle) and really brought things to life. Then into a Chang Lightspeed. Same benefit and increase in everything, but darker background. I no longer desire plugging anything directly into the receptacle. That particular Pangea seems very well built already? I tried this cheapie but goodie to very good effect:

https://a.co/d/hoNYALk

Like it even better than a Wireworld Stratus I was using prior. Gauge/shielding? Hard to say why exactly. Still (and forever) experimenting. 

A science teacher would tell me that a power cord couldn't make any difference at all. Also I haven't met a single school teacher that's in this hobby. So that was a stupid remark you made. 

Yes

Thanks for some of the replies. 

I'm curious about trying the direct into the wall VS. via conditioner in addition to trying some power cords, in a careful, sequential fashion as described. I appreciate the factor Erik mentioned about interference as a key factor.

I have heard power cords make a difference -- in a store. I do not know what difference it would (or could) make in my system.

Remaining skeptical until proven otherwise is my M.O. for this hobby, because there are many other places to make improvements. So, if I don't hear something, I will send things back. 

@brunomarcs Regarding your comment: "You think this is a viable approach?"

Viable, sure. Optimal? Not exactly the order I would do it. I would want to go in the direction which is most likely to discover which components are most sensitive to certain types of cable upgrades (clarity in freq ranges of bass/mid-bass/mids/highs/ultra highs, extension in highs or lows, etc). So, I think it would bring you more understanding by starting the experiment with all freebie 16-18awg cables on all components and rotating all available upgrade options on each component, sequentially, component by component to find which component gains the greatest benefit from alternative cables you have available. 👍🏼 I think you’ll find this method efficient and effective.

In my digital system, I’ve consistently found that it’s best to optimize cables with the best high frequencies in the beginning of the chain, the best combo of high frequencies and mids on my DAC, something similar on my preamp, and make sure my power amp has a larger gauge to optimize lower frequency response and lowered resistance. For those with the budget, the Clarus Crimson High Current 8awg occ copper power cable is a fantastic power cable for amps, especially the more power hungry solid state amps.