My thoughts on lighting, is that you install capacitors to get rid of flicker? flicker can be caused by dirty track as you say, but it can also be caused by faulty pickups (which it appears to be the case from further posts) or dead frogs and various other reasons.
My experience over 50 years of running on many club layouts, with good clean track giving good operations, until suddenly dirty wheels can bring a train to a stand. Where does the dirt come from? My guess others running on the layout bring rolling stock with contaminated wheels and share it around.
My reference to AC was purely to do with the fact that the AC power (is rectified by the chip) could not be as easily reversed for lighting control as it can be with DC operated trains, thus the need for a switch (or DCC chip) to operate correctly in the other direction.
my supposition that a well designed circuit would operate well, and a badly designed circuit would need improvements, was more directed at the Chinese, rather than SDS.
And indeed, my order has not yet turned up, as I stated, and I was only trying to help in any case.
My super capacitors arrived from China in several physical sizes and denominations and were pretty cheap ($9 US for 30 in 2012)
In future I will keep all of my experiences to myself and leave all assistance offered to more highly educated types like you.
What on earth is your problem?
Do you know something? Highly educated engineers can design a real locomotive, but have no idea how to operate them in service. I takes dopes like me to operate them in service. Experience over education any day in the real world.