A capacitor will only help filter out "noise" if the system has enough current to supply the amps to begin with. It will not fix dimming lights or other voltage problems. The resistance you are refering to is called "ESR". It is a measurement of the capacitor's internal resistance. This is the most common problem with cheap caps. If there is too much ESR the cap can actually hurt your performance. You want a cap with the lowest ESR possible.