New power cord needed for speaker with powered subwoofer?

I am sure the manufacturer provided power cords will be sufficient. Only by trying a non-OEM cord are you going to find out. Though, to me, I think it will provide a minimal change. As long as the cable provides sufficient current to the amps in the subs, those low frequencies are going to be hard to hear a difference between cables-though I expect some may disagree.
I think you should listen to your system for a few months and then consider upgrading power cords. Only then, will you be able to discern if they do make a difference.
Bob

What is the AWG of your cable?. 

What does AWG mean, and how would I find it?

Everything I have has been improved with an aftermarket PC. I don't see why a powered sub wouldn't benefit as well. If you want to, forgo the expensive makes and go with Culllen Cables or something similar. He makes great PCs for a very reasonable cost.

All the best,Nonoise