I believe that good power filters are very useful. Both to filter your AC, and to block digital noise from the digital/switching power supply components (computers, TVs, other). This means a mains filter AND a 2nd one, can be fairly simple, just for the digial /switching stuff.
Power cords i have tested many times and fail to find an value, unless you are replacing something deficient- which is not all that uncommon, but easily avoidable for $20
Power cords i have tested many times and fail to find an value, unless you are replacing something deficient- which is not all that uncommon, but easily avoidable for $20