Actually, i just realized i can use thos tiny step-down converter modules, as a replacement for the filtering cap, since those can configured to not step down voltage at all, you still get 12 volts, and a good replacement of the stock filtering capaticor.
one issue though, is that i don't know about it's current capabilities so this is something i will eventually test.
so after some tests it appears that those step-down converters aren't good for this because one can only supply up to 3 amps, with a voltage drop (supplied 12 v 18a output 9v 3a) and with this output the converter got so hot it left a burn mark of my wooden desk. so i guess surfacemounting that cap is just not avoidable..... even though that step-down converter would still be a good addition to filtering..