Double check before power on - using two PSUs

[brwainer]

I’m building a new/old system in the Seasonic Syncro case + Syncro Connect PSU. What is new is the case, PSU, and fans. What is old is everything else, including an mITX motherboard. I’ll upgrade that eventually, but I’m stuck with it for now. Problem is, the included 24-pin power cable is about 2” too short to reach an mITX mobo. I’ve ordered a 24-pin extension cable, but am looking for a solution in the meantime as this is my main PC.

 

My intention is to use another power supply (the one I was using until today) for just the 24-pin and CPU connectors on the mobo, and have the fans (other than CPU), GPU, and drives connected to the new PSU. The new PSU would be triggered on by using the included PSU tester.
 

I am pretty sure this is fine, but wanted to double check before I power it on. Should I power on the new PSU before or after pressing the power button to trigger the mobo? If I reboot the system, do I need to cycle the new PSU? I’ve never used a dual PSU setup, and I know that ideally I would have a splitter cable to trigger multiple PSUs from one mobo, but the shipment time on that would be the same as the ATX extension.

[Spotty]

39 minutes ago, brwainer said:

My intention is to use another power supply (the one I was using until today) for just the 24-pin and CPU connectors on the mobo, and have the fans (other than CPU), GPU, and drives connected to the new PSU. The new PSU would be triggered on by using the included PSU tester.

Why not just unplug the Seasonic Syncro PSU from the system and use the other PSU for everything until the new 24pin cable/extension arrives? Would be a lot easier than trying to manage two PSUs. If it's only for a few days you don't need it to be fancy, just leave the side panel off and have the 2nd PSU outside the case plugged in.

[brwainer]

8 minutes ago, Spotty said:

Why not just unplug the Seasonic Syncro PSU from the system and use the other PSU for everything until the new 24pin cable/extension arrives? Would be a lot easier than trying to manage two PSUs. If it's only for a few days you don't need it to be fancy, just leave the side panel off and have the 2nd PSU outside the case plugged in.

I know... I just don’t want to have more cables than necessary coming out the side. Unfortunately I’m one of those people who has the PC on the floor next to them (I pay attention to positive air pressure and filtering) so the less the better. Actually with so much space inside I can just put the other PSU on top of the hard drive cages.