Best Power cable around/prefer under $300....

For under $200 you won't beat an Audio Envy power cord IMO.

https://audioenvy.com/product/power-cord/5732/

I’m a big fan of Empirical Design power cables—the ED-416 would fall within your budget. I’ve been using Karl’s cables for over a decade. So many component changes over that time—same power cables. The ED IC’s are also great, reasonably priced cables—still using them after many years as well. FWIW, these are the only cables I’m aware of that won the TAS award two years in a row.

I have a Monsoon on my PrimaLuna integrated. I could easily hear a difference I liked, more tone, body and detail. You must do a home demo to decide for yourself

Go with Shunyata for sure.

You are right, they are all much better than your freebie rubber power cord. Anything, absolutely anything is better than that.  

All those other cable suggestions are probably good. There is however only one in your price range that has stood the test of time- Synergistic Research Master Coupler. Originally around $400 back in the 1990's they are still made today and come up used for anywhere from $200 on up. This makes it probably the only one mentioned you could buy and use several years then sell and not lose money.

If you like DIY and can stretch a little, you could check also a Furutech FP-3TS762, a 10AWG screened cable and copper FI-11/FI-11M connectors. 1,8-2m works perfectly fine.
G

BLE Design on Ebay. OFC 10 gauge. Rhodium or gold connectors. $39. Looks great. Sounds great. You can tell your friends it was $300 and spend the rest on music.

Definitely Shunyata. But I will suggest stretch the budget a bit, and get the Venom NR v10. 

This makes it probably the only one mentioned you could buy and use several years then sell and not lose money.

In my experience every cable I’ve ever bought used I’ve been able to sell years later and not lose money. Most used cables can be had for 50% or better off new. I’m sure the Master Coupler is ok but there’s nothing special about a SR Master Coupler in regards to resale against other cables.

What is peculiar though is if you look at usedcable.com right now you will see there are 11 Synergistic Research power cables listed for sale....more than double that of any of the 18 other brands listed in their inventory. Makes you wonder why people are unloading them in such volume or why they can’t get rid of the inventory easily either. No opinion here...just stating a fact.

https://www.usedcable.com/power-cables.html

I can easily explain this for you, based on some insider talk I know for sure: Peter, the guy at The Cable Co., which is the owner of Used Cable website, used to work for many years for Synergistic Research. Which means that’s where all SR surplus go first.

Also, typically, high volume manufacturers, not just cable manufacturers, tend to have much more listings on used market than low volume manufacturers. Similarly, low volume manufacturers, not much available in used market. This is just a fact, reality.

After listening to and enjoying lesser cables, from both Kimber and Synergistic; they were sold to make room for and finance their upper crust wares.       No difficulty quickly moving anything I've owned, from either company.         Mostly: here.                        It's doubtful that I'm alone, in that practice.

Clarity Audio Vortex...over $300
https://www.dagogo.com/audio-blast-clarity-cable-organic-and-vortex-series/

Also, typically, high volume manufacturers, not just cable manufacturers, tend to have much more listings on used market than low volume manufacturers. Similarly, low volume manufacturers, not much available in used market. This is just a fact, reality.

@thyname

Not sure I understand this logic...so this is where all SR surplus used cables go first? Makes no sense. Where does used surplus come from and what’s the difference between garden variety "used" and "surplus used"? lol

Furthermore, about the "low volume manufacturers"....Audioquest has 2 listings, Cardas 1, and Shunyata has 3. Not sure SR (and its 11 listings) is bigger than any one of these companies and certainly not bigger than all 3 combined.

Edit: In fact I just looked up information on SR. They have approx 15 total employees and operate out of a 12,000 sf warehouse. That’s honestly a much smaller operation than I had even assumed. Comparatively AQ reports to have 135 employees. 

Cullen Cable sells direct with a trial period, so you can try their 6ft Crossover cable that sells for $199 in your system to see if it works.  Underwood HiFi has their Valiant Silver cable at around $180 that might also be worth exploring.  Audio Envy has been gaining quite a following here so they’re definitely worth a look too.  Best of luck. 

Check into VH Audio and build your own. Buy the best ends/plugs you can afford and spend the rest on the cable. Chris can help you. For an A21 make it a 10 gauge cable, not 12. Don’t make the cable too short either... hopefully 5ft works. I’ve gone to Home Depot and bought bulk cable and threw on Furutech plugs that sounded great. Don’t skimp on the plugs!

I’ve owned the Shunyata’s, Nordost and Kimbers and they were fine, but for the money, especially on a power amp I’d suggest Wywires Silver Juice II HC (High Current) on an amp. You should be able to find these used in your budget or if you reach out to Alex directly he probably has a former show demo he’ll help you with. He was offering a 40% discount so you can probably pick up a new PC as well. Alex is easy to work with and very honest. Good luck.

+1 Audio Envy PCs

I bought Pangea SE cables, most used and discounted, and saved hundreds. Knowing they're better than stock cables but not exorbitant just crossed the question off my list. Some people go back and forth and compare PC's but most of my comparisons have not revealed much of a difference once I moved past stock cords. Just my experience.

I'd recommend looking for used Cerious Technologies Graphene line of their Blue, Red, or Yellow power cords, assuming you can find them in your price range.
Although you did not include the following power cord, I also believe the old original Synergistic Research Reference A/C Master Coupler power cord would work very well also.
Another option: Soniquil Power Cable by Raven Audio.
1.5/M $184
2/M $224
3/M $274
Very well built and huge bang for the buck!
https://www.ravenaudio.com/product/power-cables/

I just bought two new Silnote power cables off of Audiogon for my Parasound amp and pre for $100 plus tax each.

Cerious GE, Transparent High Performance

If you decide on giving  Nordost a try, Blue Heaven is the way to go. The power cord shares the same construction of the Norse series(Heimdall).

Obviously, it's scaled back just enough for the price point. Best buy for new Nordost users.

I really like Raven Audio power cables. All their cable are very well made at a good price.

Raven and Audio Envy are both very good, same with Wireworld Electra 7.

I have Wireworld Elektra 7. It's decent for source and DAC, not so good for the amp. Not exactly responding to the OP's needs but just sharing my experience since somebody above me mentioned about the WW Elektra 7.

I currently do not have any power cords in the $300 price bracket other than the WW Elektra 7. I have two Acrolink power cords which cost 10X more than the Wireworld and the costlier cords surely sound better. Fortunately!

Splurge and get the audioquest thunder....

Thats a lot of money be very carful.

"Splurge and get the audioquest thunder...." I replaced six AQ Hurricanes with Clarity Audio Vortex power cords after comparing them in my system. I've listened to Shunyata Alpha & Sigma, Wireworld Platinum, and AQ Dragon power cords in my system. There are no absolutes in Audio, but I prefer the Vortex power cords over everything I've heard in my system...detailed and very open soundstage.

+2 for Audio Envy!
You won't get more "bang for the buck".
Also 45 day trial.

One of our audio club members tested several power cables and he recommended the Shunyata Research Venom HC V2 Power Cables. I have them for my Marantz PM-KI and SA-KI RUBY integrated amplifier an SACD Dac. I found a special package deal of a 3 cable bundle.

Might consider Audio Art Cables pcs, a couple models within your price range; and looks like there presently is a sale. I’ve been pleased with them in my systems.

I have an Audio Envy cable; absolutely loving it. 

Anticables...absolutely top notch!

Agree with both Anticables and Audio Envy.  Very good values.

Audio envy +1

Definitely the Shunyata

A Signal Cable Silver ( $170 ) replaced my Shunyata Python Helix on my Hydra 6

After communicating with several Audiogon members I decided to contact Audio Evny and I ordered a 6' Mega 3 power cord with 6 conductors.
I had to wait about three weeks for it to be made but I can absolutely say that it was worth the wait. Very lightweight, flexible, and well constructed, visually looks great.
After four days on my Audiodharma cable cooker, I installed it on my Allnic T-1500 300B Integrated tube amp. Wow! sounds great, now I understand the high praise that I was reading in the forms. I highly recommend the power cable.

Hi Iak,
I was looking at the Ocean Elite 3 power cord. what was the deciding factor on choosing the magna? Thanks? I recently purchased the Anti cable PC and I must say, it did make a huge difference in base and sound stage. I am surprised how much of a difference a PC can make.

Hi matt00,I recently added a level 3 Anticables PC, I noticed the same outcome as well.  It only took me a couple years to find a used one at a very reasonable price. 

Anticables or Signal cable!

@matt00, I chose the Mega strictly based upon the suggestions of other Audiogon members that have heard the various AC power cords that Audio Envy make.

@matt00

Another vote for Audio Envy Mega 3. As @lak pointed out, Mega 3 uses twice the conductors than Ocean Elite 3p and recommended for any high current electronics like amps, integrated or power conditioners.