im not doubting your words. but i had my lights dimming when my car's electrical system was at full load. putting in a 1 farad cap cured it.

before cap: stereo on full blast, headlights on. headlight and dash lights blink on every bass hit.

after cap: stereo on full blast, headlights on. very little or no blinking.

but* i know my alternator is getting old. even without the system on, with my headlights on and me powering the window up or down, the engine has to rev a bit to get some juice.

so i think a cap is a temp fix in some cases. if you can afford an upgraded or rewound alternator, that would definitly be my choice.