Power Cords/ Conditioner/Surge Protectors

Everything matters. 
I have experimented with several power cords.
generally speaking the better the equipment and the power supply, the less you need exotic power cords. 
However, all of my equipment has some level of upgraded power cords.

That said, if you stream, I highly recommend a high end network box to clean up your Ethernet signal.  I have used the UpTone Audio Etheregen and love it. Easily matches any power cord upgrade I have made for less money in most cases. 

I was going to get a Puritan PSM156, but saw reviews of the Kinki / Vinshine Tai Hang Power Enhancer.  Bought it and am so impressed, I bought a second one. Tai Hang Power Enhancer

@roadcykler 

AC cables are 100% objectively audible, and often measurable, I wish it wasn’t the case, but it is.  Shunyata Research is the best stuff imo.  And a great value compared to the field of options.  

I will admit upfront that I am a Shunyata fanboy . . . not because I get paid or sell them, but because each cable that I have put in my system has elevated the sound quality, starting with my Sigma power cable for my ARC REF 6 pre.  A clear and easily audible immediate improvement over stock.  My MSB Discrete/Premier Power supply was next and then the Pass 250.8 amp.  Each power cable made an improvement, although it was most obvious with the ARC.  The Sigma speaker cables were next.  A very audible improvement from Shunyata's already good Alpha v.1's.  But as I have said on other threads, putting in a Shunyata Everest power conditioner really was like putting in a new component into the system.  Everything sounded better, from soundstage width and depth to placement of the instruments, to a "black background" for the instruments.  I was very surprised.  Plus, as an added bonus, I had a lightning strike that fried my entire HVAC system and generator, but nothing happened to my stereo system since everything was plugged into the Everest.  So I can recommend Shunyata easily.

However, cables are also system dependent.  The higher end your system, the more you will notice a difference.  The less resolving your system, relatively speaking, the less of a difference you will notice, obviously.  But I speak only for myself, from my experience. YMMV.

No. None of those things will improve the sound of your system, but they may hurt it. Anyone who says different ignores science, physics, and/or could be one of the many snake oil salesmen ruining this hobby. They're straight up liars. Wish this industry had some regulations...