Power ‘filters’ are terrible, they normally take more away than help the sq. You want a power regenerator or use balanced power to get the best out of your system.
How much to spend or how much improvement you are going to hear all depends on the quality of your system and your hearing. To actually state the a $20 cable is all you need is foolish for example, even a pioneer system would probably see an improvement with a $20 cable. A dealer friend did a demo for me on a system that cost around $20k. He made 1 change that I couldn’t see what he did and it made a huge difference in sq. All he did was to replace the stock power cord on the Mcintosh amp to an entry level red dawn nordost power cable. This was almost 20 years ago and ever since, I have always used the better power cords on all my components, which have been much more expensive than the red dawn
How much to spend or how much improvement you are going to hear all depends on the quality of your system and your hearing. To actually state the a $20 cable is all you need is foolish for example, even a pioneer system would probably see an improvement with a $20 cable. A dealer friend did a demo for me on a system that cost around $20k. He made 1 change that I couldn’t see what he did and it made a huge difference in sq. All he did was to replace the stock power cord on the Mcintosh amp to an entry level red dawn nordost power cable. This was almost 20 years ago and ever since, I have always used the better power cords on all my components, which have been much more expensive than the red dawn