[AFBeefcake]

Its just a capacitor of around .5 farads.

Yes a capacitor will stabilize the voltage, but unless your ruining subs and amps, You real would not need one.

A capacitor resists voltage change. As the voltage across the cap drops the cap tries to make up for the difference by suppling voltage.
The bigger the cap the longer it can make up of the difference in voltage. once the voltage across the cap is back to normal the cap recharges.

A capacitor really only helps when voltage draw is continually changing.
Like with a sub woofer amp, when the sub hits is draws power. The harder the hit the more power drawn.