It can be a tough subject. But generally speaking, if you bought a reasonably made amp then it already has enough caps built into the power supply for it's needs. No need to be redundant.
If people REALLY need something, here's a 1 FARAD cap. Use 4 of them for 12.5V which is ~where you're charging state takes place, usually a bit higher though. You can hide these guys too. *shrug*
105CKR050M by ILLINOIS CAPACITOR - Buy or Repair at PLCCenter - PLCCenter.com
Their original use was in a sound quality competition. Power regulation wasn't able to respond as quickly due to design and they would add capacitors to the lighting circuits just in case because a lot of "sound quality" competitions is based on maintaining safety and OEM specifications while adding the "experience" to the vehicle. These days, power regulation is built into the alternators and the system is able to handle power spikes much more efficiently.
Dimming lights and other occurrences are typically due to poor grounding points.
