Power cable suggestion for Classe CA300

I am just extrapolating my own results, but I suspect the Zcable Thunder would be a great cord on just about any amp.

Zcable Website

Powercables should not really have a sonic signature. They should allow the amp to do more of what it is designed to do. The times when differences are heard, IMO that is due to one of the PCs allowing the amp to do more of what it is designed to do than the other PC or PCs. BUT I could be wrong.

In my expereince PCs can offer a lot of improvement, or virtually none depending on the quality of the PC, and the quality of the power supply. All of the PCs I have now are diy. I had some manufactured PCs but I replaced them with the DIY and thought they sounded better. I have to admit I have never listened to a Purist Dominus, or Shunyata, or any of the other high-buck PCs. They might be lots better than what I have.

I use an LAT International AC2 with mine. To my ears its sounds better ( A little smoother ). As always YMMV.

Although I am a broken record on the topic, please try Lloyd Walker's SST contact enhancer on any power cord you end up selecting, and you should look forward to hearing more of what your amp is designed to deliver. Admittedly, I have not heard your particular amp, but this stuff hasn't failed yet on multiple power cords with multiple components.
Disclosure: I did originally purchase after meeting Lloyd Walker at the NYC Stereophile Home Entertainment Show, where his hypnotic personality resulted in my purchasing seventeen jars, and becoming a tireless booster. No, not really :>)

I like the PS Audio Extreme Statement on my CA 200, improved the entire frequency range.

If you don't have a dedicated line for your Classe amp I would consider that first before a power cord upgrade.