I have the 1125W power supply.
HP: "The 1125W Power Supply can also supply 1450W of output power when the input voltage is greater than 180V under all conditions".
I'm in Australia where our output voltage is greater than 180 V so power supply is not the problem.
I have a feeling that it is a BIOS update as I am using the high end CPU and I have not done any update as of yet.