It is almost always better to get a aftermarket power cable.
I use them almost exclusively in my builds.
This is because I don't need 6' of power cable and it is hard to hide the four extra feet that I don't need. So, I use 1', 2', and 3' power cables from Monoprice at about $1 or so per cable.
Anything more expensive is just throwing money in the garbage. Don't do it.... as you've been told.
Not sure what subwoofer you got, or how much power you've set aside in your home specifically to run the subwoofer, or any of your AV gear for that matter, but a power cable isn't a magical device and never will be. Just use the cable that came with it, which was designed to work with it from the start, or pick up something shorter, of the same gauge, which will work equally as good.