[SOLVED] Motherboard doesn't POST after shutdown or restart unless I turn off and on the PSU, then it boots fine

[Cariote]

If I turn off and turn on the PSU, the PC boots fine however if I shut down or restart, it doesn't POST at all, but the fans are running and the Q-LEDs light up red, yellow and then off and nothing happens after that until I restart the PSU again, and then it boots fine again.
Here's a video showing the problem

I've tried:

• Reseating GPU & RAM
• Resetting CMOS
• Unplugging everything (SSD, GPU, connectors, etc.) and booting by shorting pins
• Updating BIOS to latest version
• Testing front panel pins

Note that this is a new build, most of the parts listed were recently bought a few days ago, and since it boots up fine after I don't think it is the PSU causing the problem.
Maybe I can change a BIOS setting to fix this?

CPU: Intel i7-12700K
Cooler: beQuiet Dark Rock Pro 4
Motherboard: ASUS TUF GAMING Z690-PLUS WIFI D4
RAM: ADATA D10 GAMMIX 3600 8*2GB
GPU: MSI GTX 1060 6G
M.2 SSD: ADATA XPG SX8200 PRO 1TB
SATA SSD: Kingston SV300S37A120G 120GB
PSU: Corsair CX550M 550W

 

[COLGeek]

A defective PSU will cause these sorts of issues (the switch flipping is the clue).

 

[Satan-IR]

and since it boots up fine after I don't think it is the PSU causing the problem.

On the contrary, as COLGeek already said, that is classic failing PSU behavior.

 

[vov4ik_il]

I would try it with a larger PSU for starters...