Should I upgrade the cable of my Line Conditioner?

There are a lot of companies that sell direct with generous trial periods and offer a lot of value for the money (Triode Wire Labs, Cullen, Morrow, etc.) so it’s easy to just try some for yourself.  The other option is to buy used and just re-sell if they don’t work for you.  I agree 100% with @ozzy that EVERYTHING matters so read reviews, pick a PC or two that provide the sound qualities you’re looking for, and go for it!  Best of luck. 

I do not have much knowledge with electricity.

But I would use a power cord that gives a lot of rooms , for high power peak demand.

Such as for subwoofer , powerfull amplifiers , etc.

I use PS Audio Perfectwave AC 12 power cord. 8 gauge.

You may find more refined power cord , but I am sure that with a 8 gauge,

it will be enough.

My power conditionner has 8 outlets , fully used  with power amps ,subwoofers ,  for my Home Theater system.

No. Furman supplies a suitable cable. Replacing it will be a waste of money.

I was told that the manufacturer only supplies a power cord that is good enough to get you started until you can save enough money to buy a better power cord. Does this not hold true for the original cord that goes in the power conditioner? Wouldn’t that be the original sin? Why don’t we need to replace the wiring inside the wall?

Just replaced the wiring in my wall.  10ga to the service panel.  Recommend 10 ga power cords for amps.