[SOLVED] Separate PSU for CPU

[CuriousNerd]

Hi,
Reaching out for some assistance with powering my system safely. I have the following build:
ASUS X570 motherboard
5900X CPU
Dual 3090 with NVLink
64 GB RAM - 4 modules
2 NVME SSD
Water Blocks cooling CPU, GPUs
Water Reservoir and Pump
10 AL120 Fans in Case

The max system power requirement is approx. 1100W. I initially had a single 3090 and was using a 1000W PSU but recently upgraded to 1500W PSU after dual 3090 setup with water cooling. The reason I am reaching out is that my 1000W PSU is almost new and although I have replaced it with a 1500W PSU I would like to understand if there's a safe way to use 1000W with another PSU.

The major power drawing components are CPU (TDP 105W,) 2 x 3090 FE (TDP 350W x 2). During heavy model training and stress, I have seen GPU reach 355W.
I also did some research on using a dual power supply with an Add2PSU chip to power my GPU. The idea behind this chip, as I understand, is that if anything goes wrong with the PSU providing power to the motherboard then it will send a signal to the second PSU to turn off. Even if it can be done, I read that it's not safe to supply separate power to the Graphics card as it draws a max of 75W from PCI-E and remaining from Card's power supply and where and how much it will draw power from is unknown. So in case the PSU giving power to the graphics card goes bad, it may damage the card with only power coming from PCI-E.

The question I have for the forum and have not found an answer during my research is if it is safe to provide power to the CPU and Water cooling block using a separate PSU (650W) and power the motherboard and my dual 3090s with 1000W PSU. Here 1000W PSU will be main with 650W attached to it via Add2PSU chip. 1000W powers motherboard via 24 pins and both GPUs, 650W powers CPU and water cooling. I read that one 12V pin from 24 pin motherboard do supply power to CPU but the main source is the 8 PIN connector dedicated to the CPU. If I go with this configuration then I would like to get an opinion on if this is safe. Safety first. This approach saves me buying a $500 1500W PSU as I can use my existing 1000W PSU and supplement system with an additional 650W PSU (max. $150).

Thanks for reading this question and for your advice.

 

[John Chesterfield]

Bad idea, get the upgraded power supply.

 

[GoboII]

In general, TDP isn't a valid measurement of power draw. Notice that the 11900K has the same TDP as the 11600K, though it should be pretty apparent that the 11900K will draw more power.
As for using multiple PSUs in one system, it can be done, but the way you're suggesting probably shouldn't be done. It's fairly common to see two PSUs in one system in, say, a server, but this is for redundancy, not to increase the maximum power draw. If you found a way to isolate it so that components are only getting power from one unit at a time, you could, but at that point, you will have probably invested enough into it that you may as well just get a bigger PSU.
For a 5900X and two 3090s, a 1500W power supply is fine.