ok here's another way for all of you to think of it:

he is adding a cap to his entire electrical system.

now that doesn't seem so bad, does it? but guess what? that's the same thing. if the fuel pump is already rewired and you're adding on a cap it's the same as installing a cap right next to the battery in parallel. the electrical schematic would look the same whether the cap is next to the fuel pump or in the engine bay next to the battery. for some reason you guys seem to think the cap is going to be selective and only help the fuel pump and tell the other electrical components to fuck off.

the reason for adding a cap to your audio system is not to help your sub. the purpose is to help your car's electrical system. claiming that cap's are only for audio is dumb. yes your 2000W amp is the cause of the problem, but the main benefactors of the added cap are the auxillary components which are being robbed of power (i.e. FUEL PUMP). caps are only associated with audio because high output amplifiers with exteremely large instantaneous power draws are the most common reason for needing a cap.

i'm not saying this is going to make a world of a difference but if he has measured the voltage getting to his fuel pump and found it to be dissatisfactory then i don't understand why you guys have such a hard time understanding why a cap would help to remedy this problem.

-marc