Moon,
All the suggestions are very good that have been presented, Having good equipment always helps but it is always subject to the environment it is in.
I think the underlying issues here are a few items. What no one here knows and you are probably the only one who cares and really needs to know is how "clean" is the power presented to your audio system including your speakers. This, to me, is really the determining factor on whether you use after market power cords or not. Lets say your power and I mean AC power (noise included) to your equipment, is real clean, which is unlikely unless you are already filtering or cleaning it somewhere before, then using an after market power cord will not provide you with enough cost effective value versus improvement. This is of course a judgment call and sometimes a perceived improvement.
If you are like most of us, the power is noisy at some level whether it is in the line itself coming in the from the street or getting "transmitted" across the lines within the house from other devices in the house such as a refrigerator, washing machine, wall air conditioner, etc. Getting some type of line filter, line stabilizer, regenerators, line cleaners or any combination/variation of this will also help/improve your "sound" but again only to a point. After market power cords do help in situations where there is noise, interference or whatever you want to call it. They will act as pseudo filtering devices in this function and will appear to improve your sound. A combination of any or all of the above can be an improvement but again how much is really needed and at what cost is your call.
The level of improvement usually appears in more "black", quieter noise floor or the "appearance" of greater dynamic changes from low to high. This is not sound levels but the overall presence within the tonal swings and lack of noise or cleanliness within the sound. The most important thing here is to realize these "differences" are subtle at best and very rarely anything else.
You are the only one who can decide how much needs to be done and when you hit the wall of diminishing returns. This is where spending more money will not provide enough of a improved "value" in sound reproduction or reduction of noise level. Which product you buy is a preference based on locality, availability and a certain amount of personal taste.
I do not think you can go wrong with any of the suggestions. Personally, I have some after market power cords and also some which I have made. Can I tell the difference, well, yes, but only a very slight difference between a $350.00 power cord and one I made for about $50.00.
Good Luck and let us know
Jeff