Did some more testing and had a crash with the pure ATX power supply. Also swapped out the C13 power cable.
The issue is definitely the motherboard/cards -- when the system crashes, the cards draw way too much power if not completely powered down.
Current setup now:
110 V -> DPS-1200 -> Power GPUs and 12v EPS
|---> Pico PSU ---> 24 pin ATX + SATA
100 Mh/s @ 427 W
