I was looking for a high farad capability cap and got discouraged when i saw the Rockford one for 400 bucks. but then i saw the Power Acoustik ones on ebay for every cheap - even 70 dollars... and even 40 farad. do these work properly? And if not, what about the tsunami ones? I saw one hi-farad Tsunami one on ebay which has the exact same chassis as the rockford one. but they are about half the price.