Modded PC power supply for charging

hmm wow this supply i guess isnt powerful enough for it then. i found this one in my room so that means im looking for 600w power supply? i think i might have another one with more wattage. even if i have to go out and buy one its cheaper than buying and rc car one.

also i know this might sound stupid but what if i combine the 12 volt and 3 volt wires to make 15 volt??? or that isnt possible? thanks again