Your PSU is not on that list the one on the list is AX860 not AX860i but anyway that should not matter, the reason for you to test the board outside the chassis is to ensure that the board is not shorting somewhere on the chassis.
So that's why you need to remove the board from the chassis and test it with minimal components outside the chassis (With One RAM Stick, Board And Power Supply Only) Use the on board HDMI if possible or thunderbolt which can act as Mini Display Port if you plug a Mini Display Port connector to it.
Afterwards if all goes well add each component one by one till you get the culprit all outside the chassis.