have you checked to see how much each of the rails provides or if its a single rail PSU? possibly you're exceeding the rails supply
Sadly, Dell doesn't seem to make that info available, but it's very possible that this is the case. The system is supposed to support 2 graphics cards, but the PSU only has 2x 8 pin and 2x 6 pin connectors available. And I need 4x 6 pin connectors.
Here is the info that I could find.
POWER
NOTE: The T7600 utilizes an Active Power Factor Correction (APFC) power supply to enhance efficiency. Dell recommends only Universal
Power Supplies (UPS) based on Sine Wave output for APFC power supplies, not an approximation of a Sine Wave, Square Wave, or quasi-Square
Specifications
Power Supply Wattage
1300W (for AC input voltages of 181—240 Vac)
1100W (for AC input voltages of 108—180 Vac)
1000W (for AC input voltages of 100—107 Vac)
AC input Voltage Range 100 - 240 Vac
AC input current (low ac range/high AC range) 14.0 A / 7.0 A
AC input Frequency 47 Hz / 63Hz
AC holdup time (80% load) 16 MSEC
Average Efficiency (Energy Star 5.2 Compliant) 87 – 90 – 87% @ 20 – 50 – 100% load
DC parameters
+12.0v output 12VABCDEFGHIJ ; 18.0A
+5.0v auxiliary output 4.0A
-12.0v output 0.5A
Max total power 1300W
BTUs/h (based on PSU max wattage) 4113.0 BTU
Power Supply Fan 60*25mm (x2)
Compliance:
1watt requirement Yes
Climate Savers / 80Plus Compliant Yes
FEMP (CECP) Standby Power Compliant Yes