Am i missing something without a power conditioner?

I own a Furman REF20i I bought used.
I also own a PS Audio P600
And I use aftermarket power cords.
The conditioner can help.
You really need to hear it for yourself.

General improvements with a conditioner are clarity and finesse.
Losses can include less bass and less midbass. Going to a lean sound compared to no conditioner.
The bass may seem like less, but really it may just be TIGHTER.

@erik_squires

Won’t disagree about power cords, Eric, but my milage has differed, if just a little. I heard a small difference, or thought I did, but markedly less than with the isolation transformers, where the difference was obvious.

But bang for buck? Nossirree. I would buy them, if I didn’t have a better solution already, somewhat after my third premium MC cartridge. And the big Koetsus DO make a significant difference, no "thought I did" about it.

As I said in other forum, my experience was at first  with passive AC filters. First with Lessloss, Acoustic Revive, Bybee (two of them). 
When I tried the Torus AVR16 in which I connected my whole system incl the tubed mono blocs Air Tight ATM3, this has been « end of the game » for me.
 Dynamics, silence, transparency, images in all dimensions, music flows very naturally in the room...
You just have to be be carefull dimensioning the transfo. In Europe, Toris doesn’ sell their balanced models, but if you are in USA this is a possibility you can explore.
My 2 cents 

PS : another thing to consider if you don’t want to « miss something » is the Total Contact. It is a contact enhancer that is really (I mean Really) efficient. I won’t say more because the topic can be polemic.

AudioTroy.....Richard Grey was the worst component I've ever had in my system....  Ruined the sound...couldn't wait to get it out.  (Ayre/Vandersteen)

Missing something? Probably yes, a lower noise level. Depends how good are your power supplies in your system and how much noise filtering are they doing. I don’t see what difference can make the power cord, the noise still goes through.

In my case I use a Furman PST-8DIG and I clearly noticed complete silence under no load using Marantz SR5008 and 7008 receivers. Plasma TV is making way less hi frequency noise. The filter inside is working even if doesn't look more than a power bar.