I don't know the first thing about capacitors but I want to get one, I am running about 600 watts steady to my sub and wanted to know what a good capacitor to get was. and wtf is a farad?

Basically I want to do this because I already blew an alternator, I'm assuming that getting one of these will weaken the strain on my battery and alternator right?

 

It'll help a bit, but it's not an end all. Get a 1farad.

Farad is a unit of measurement. A .5farad or one half farad is good for systems upto 500watts. A 1farad is usually good for systems upto 1000watts. So your over the 500 but under the 1000, so the 1farad is the good choice.

Get a name brand. I got a Rockford Fosgate one on ebay for $70shipped.

 

If you blew your alternator, did you get a new/higher output one??? That would have been best...