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