a cap will not make subs hit harder, it will not make lights stop dimming, they are 100% pointless
i USED to have a cap at one point, my voltage at the amp with the cap was 14.1 (battery was 14.4 at that same time) cap voltage read 14.4 as well, however beyond that it had a decrease in my voltage, lights STILL dimmed (which i knew they would anyway) i remove the cap, i had a solid 14.4 going straight from the front battery all the way to my amp. also when i had the cap, i was seeing voltage drops as low as 12.5 volts, without it.. the lowest i have seen is 13.1 @ full power.
as far as subs hitting harder.. when an amp has higher voltage it is able to produce more power, when an amp has lower voltage it tends to put out less, now if a cap can decrease voltage to the amp then it is putting out LESS power than if the voltage was higher
so say my amp put out 500rms @ 14.1 volts (when the cap was in-line) then i remove it, saw 14.4 volts, which the amp put out 600rms @ 14.4.. going by this, the amp would put out more power WITHOUT the cap, therefor the subs will hit harder and be louder based on this (due to having MORE power than less), however even if a cap did happen to add power, it would NOT be audible to the ear so how would he know it hits harder and gets louder?only way would to have an ACCURATE METER, being a term lab because another 1-200rms wouldnt be audible to the ear when having 1200rms or so or whatever, maybe stepping from 200 rms to 400rms, but a cap would NOT be able to supply the much more "power" or even voltage to the amp ... they just add resistance IMO.. paperweight FTL
just my .02
