the radeon hd 7770 has a max tdp of 80w(5w more that that supplied by pciex16). so it does require additional power supply 6 pin pcie
as for capacitor aging.yes capacitor decays,but in gpu they use very high quality ones,if you should be concerned about capacitor aging it should be on your psu,if its low quality, solid psu manufactures like cooler master psu's uses very high quality Japanese capacitors.so buy a good powesupply,if you are so concerned of capacitor aging