Question 3090ti Refuses to allow pc to boot up?

[MykiLive]

Hello I recently got a 3090ti and I wanna figure out if my 3090 is broken or if it’s my power supply. The PC boots up with the 3090ti plugged into 2 ports of the PSU but not when the third one is. The power supply still delivers power to the pc but doesn’t turn on (I know this because the motherboard lights up). The GPU lights up as well when not fully plugged in with the PC on. I have updated the bios tried different cords, and tried different plug ins around the house. Does it sound like a PSU or GPU issue to you guys? If it’s PSU what should I upgrade to 1000 or 1200? I don’t plan on updating this PC to a future GPU after this I will most likely just build a new one in the future. The recommended power for this pc was 779 after the 3090ti upgrade on PCPartPicker.

PC build:
Be Quiet 850Watt Plat
Corsair Vengeance LPX 32GB (2 x 16GB)
Tuf Gaming Z690-Plus
Scythe 2 Rev B
3tb HDD with a 250GB SSD
3090ti trio fans MSI
I am updating from a 1080ti founders edition

 

[MykiLive]

I would also like to throw in this is the first pc I built and my 1080ti came from a prebuilt I bought in 2017 I built this PC back in March and also had issues setting up the GPU pretty much identical to this accept the issue was the bios which I already tried updating to version 2004