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

They certainly do work in conjunction with a power strip from my experience. I don't use a power conditioner, so I can't comment on that.

In my experience, power cables always affect the sound, no matter where in your system they are. The more length, the more they seem to impart their sonic characteristics. After tons of testing, one could probably approximate a connectors/plugs to cable length ratio for how much each affects the sound. The plugs/connectors on very short power cables affect the sound qualities more than those on longer cables, so it seems they have more of an absolute or constant effect which is relative to the effect resulting from the cable length.

If you want to do your own testing, get some adapters and daisy chain different cables together to get really deep into this. The cable used to feed a power distributor/conditioner demonstrates the same effect as a direct daisy chain. And I’m not totally sure about this, but cables that plug directly into upstream components may have greater sonic effects.

I know my cables and components really well now and how they interact, it just required lots of different combinations, time, and a keen ear to discern the different qualities that they impart on the whole system’s sound. I would suggest moving forward as if every single cable contributes it’s own sound qualities to the whole. Any cable in the chain that lacks clarity or adds graininess will compromise the end result.

If you do get new power cords, try them with and without the conditioner. 

I think you'll have trouble improving on the Pangea AC 9 SE.