AC cord for Manley Chinook...

Power cables are important, and your Chinook certainly deserves a good PC.  I’d say budgeting around 10% of the component price is reasonable as to how much to spend, but the most important thing is that it provides the improvements and sound characteristics you’re looking for.  Read reviews to see which ones sound like they offer what you’re looking for and go from there.  There are some good manufacturers who sell direct and offer generous trial periods, and that’s what I’d do if I were you.  Here are a couple that are highly regarded and worth exploring…

https://iceageaudio.com/ice-age-audio-store/ols/products/ofc-power-cable/v/OFC-PWR-CBL-5FT-LNG

Here’s a review just fyi…

https://positive-feedback.com/audio-discourse/ice-age-audio/

https://triodewirelabs.com/product/eleven-plus-american-series/

Hope this helps, and best of luck. 

@larseand Manley gear is always great, and the Chinook is a classic! There's a reason it has been on the market for years. 

I would think a component of that caliber would benefit from a power cable upgrade in general. Back in my vinyl days I always felt like I had best results from AC cables that focused on robust shielding to keep noise out of sensitive components like phono preamps.

Recently I picked up the Veritas Cables Aeris on all of my components and have been really happy with them. I'm all digital now but I bet it works just as well for analog. They mention a multi-stage shielding system so that would probably be a good fit.

https://veritascables.com/products/aeris-power-cable

As soix mentioned above, you always want to make sure you get a trial period. I wouldn't buy from a brand or dealer that won't offer such a program.

So the OP believes that there is some bad electricity getting past the Pangea into the Chinook? Really! Inquiring minds want to know how this is possible!

just to ruffle @jasonbourne71 feathers. 
https://bellasoundaudio.com/kaula-ac-cable.html

I recommend trying an Audio Quest Hurricane. If you want quiet, transparent, dynamic sound. Exactly what the Hurricane did for my Audio Research amp. I spent a year auditioning different cords, and each tipped the tone or was not as dynamic as the Hurricane. This cord has swept the audiophile community over the last couple years. 

Love the Bella list of features, including: "Enhanced Quantum Purification Core Technology" Wow, that sounds really cool.  

Also, this is a great video by Cailin Gabriel of Shunyata

9:30 minutes in he addresses the question of how can the last six feet matter:

https://www.youtube.com/watch?v=MpAsUgv24jc

@ghdprentice The AQ Hurricane is a nice cable as far as the big mainstream brands go. Probably the best value I've found from that group. I always felt it worked better for amps than source components.

I personally feel you get way more for your money with the smaller brands like Audio Art, Triode Wire Labs, Veritas Cables, or Finley Audio to name a few. But as always it is system dependent.

Great results using the Analysis Plus Power Oval 2 power cord with that Manley Chinook.

@v-fi

I agree they work best on amps. I actually use Transparent interconnects and power cords on all my other stuff.

I certainly understand why folks would seek saving money via off brands. I personally found it hit or miss so much that in the long run (unless your doing exploration just for fun) it is more cost effective to buy mainstream. But there are more than one approach as there are different motives and kinds of people. 

@ghdprentice

I do like adventure and trying out brands that are maybe off the beaten path. But that has always been rewarding in my experience. Not that there is anything wrong with more mainstream stuff in some cases.

For example I feel like Dynaudio has enough expertise and capabilities to make world class speakers. Can a DIY team make a better speaker in their garage? Not likely, but they may well still come up with a truly enjoyable speaker anyway.

Cables (and to a lesser degree, audio streamers/servers) seem like a different thing though, were the DIY team actually has a good chance of matching or exceeding the big guys. At least that has been my experience with those. But cables are so easy to demo for such low stakes (assuming a good return policy) that I figure why not?