I have your X8STL-IF motherboard and CSE-813MTFTQ chassis with PWS-521-1H power supply. The manual states “use a power supply that contains a 24-pin and two 8-pin power connectors”, but I have a new PWS-521-1H power supply that doesn’t have two 8-pin connectors. Looking at your 6016T-MT server, it has this motherboard and power supply, so how do you suppose to make the connections to the mother board when this power supply doesn’t have them?
With Supermicro power supply it does not require to use two 8pins EPS12v. You can use one 8pins EPS12v and one 4pins EPS12v header connected to the motherboard.