First idk what DDU second yes i have 550 psu corsair 2x8 pin connector and the gpu was used the guy send me the gpu with the buying receipt and my system is
CPU i5-3470
RAM DDR3 1600 8gb
MOBO https://www.asus.com/Motherboards/H61MAUSB3/HelpDesk_Download/
BTW i don have other rig i had old gpu it works fine it just this gtx 970 that i plugged it from DVi-I slot to vga with adapter