Question Unusual boot issue

[Alanr1111]

Hi all, anyone got an idea what's going on here?
If I power on via the power button as normal I get no video and all cooling fans operate at full speed and it fails to boot.
The remedy that works for me so far is that I must first allow this error to occur, power off the machine via the PSU, wait around 10 seconds, press the power button while the system has no power and then power back on the PSU and hit power button again. After this the system boots as normal and operates just fine.
If I fail to wait the 10 seconds or so after powering down the PSU then the error returns and it's no video/fans on full again. The same happens if I do not press the power button at least once while the system has no power.
You can reset the system via windows and it resets and reboots as normal but no matter what it will fail to boot from powered down state unless I follow the specific steps I mention above.

Got to be some kind of power issue right?
Can't remember precise full specs right now but it's good brand 700w psu, rtx 2070, modern CPU, 16gig ram, Asus tuf motherboard modern system.

 

[rgd1101]

open the pc.
what the good brand 700w make and model?

 

[Alanr1111]

open the pc.
what the good brand 700w make and model?

Ocz 700w. Not best of the best but not cheap junk either.
Problem began when I swapped out motherboard and cpu for new upgrade but had this PSU a few years now.