Power - where to start? Mains, chords, conditioner, filter?

I also live in an apartment and greatly lowered my AC noise floor by powering all my gear from a balanced AC power supply from Equitech, the industry leader .
 Modifying the wiring and plugs in my place were not options without risking eviction .I did later make my own power cords using Oyaide's Black Mamba cables and gold plated copper plugs and iec connectors to great benefit .

A side benefit was that the colors on my television also became richer , with blacker blacks . YMMV

In my opinion, the place to begin is with one or better yet two dedicated circuits with 20 amp breakers and wire runs of 10 gauge although 12 gauge would work. In addition to that use high-quality AC outlets.

Agree completely and that's exactly what I did when I set up my current main system (I located the system in the next room to the main panel).

I use a filter (Inouye - http://inouye.ca/index.php?page=Products) on all front end source equipment (sources, phono preamp, preamp), which makes an obvious improvement, but not on the power amps, which suck too much to go through most power conditioners.

I've done the dedicated circuit,  regenerator,  and selective power cords. The P15 made the biggest,  monumental changes actually, improvement. Dedicated circuit couldn't hear the diff, but then I'm running through a regenerator. Power cord between the wall and regenerator was the most significant PC upgrade, dac next.

Regenerator helps a lot in my case, I have older PS Audio PPP, but it is not enough when wall current is very bad. Possibly their newer units are significantly better. But again, there is no substitute for great equipment. Power cord on regenerator is very important, I can confirm.

My approach was haphazard but each step improved SQ - 
- Room was already on dedicated circuit, only 15A though.
- PS Audio line filter/surge protection.
- Replaced power cords - each one made a step change improvement, currently have Cardas Clear for amp, Audioquest NG4 for filter/surge, and Acoustic Zen Tsunami for DAC.  Fun to try different cords, all purchased used.
- Replaced outlet, using Furutech mid level rhodium.
- After replacing outlet, plugged amp directly into outlet, although I am not 100% sure I would be able to tell a difference in blind testing.
- Still need a cord and filter/conditioner (and outlet?) for the modem supplying the Tidal signal.
- Probably will get a second furutech outlet when I have more equipment to power.
- Thinking about one of those ISI parallel filters (Music Direct, $99, seems like a no brainer, but then I'd also need a second outlet and of course then another ISI, amazing how costs run away in this hobby).
- Also thinking about fuses for the amp.
- Mildly embarrassed that I have done the above yet never cleaned the connecting points for power supply, interconnects, or speaker cable.
- Total regeneration makes perfect sense to me, very common in industries and applications where clean power is a must, this just hasn't risen to the top of my improvements list yet.

Each step made an improvement, the biggest to my ears was the power cord for the amp and the outlet.  I hear more detail including resonances (so less noise), and better micro dynamics (which I guess is also less noise?). 

I have reached the conclusion that like a lot of things in HiFi, the more research time and money you put into power, the more you will benefit. 

Agree that power improvements often have the highest ratio of better SQ per $.