wrx90 two psus, which one to connect to gpus?

[iedoc]

I'm assuming you'd connect psu 2 to the gpus, but its important to be sure about this since each psu may be on a different phase so the pci slot and the pci cables must be on the same phase

What is exactly powered by each psu? both psus connect to cpu inputs and cpu pci inputs, but only the first psu connects to the two 8 pin pci power inputs next to the atx input, so because of this it almost kind of seems like the first psu should be the one powering the pci devices (gpu). The manual only says how to connect the two psus to the motherboard but says nothing about what each psu is powering or how to hook up pci devices in dual psu mode

[Aureliannn_ASUS]

Hi @iedoc ,

thank you for your inquiry. In dual PSU mode, each PSU typically powers different components of the motherboard to balance the load and ensure stable power supply. 

Regarding the specific devices powered by each PSU and how to connect PCIe devices in dual PSU mode, we recommend referring to your motherboard manual. You can consult the quick start guide below, which provides detailed connection instructions. 

Q22563_Pro_WS_WRX90E-SAGE_SE_QSG_WEB.pdf (asus.com)

Thank you.

[iedoc]

hi @Aureliannn_ASUS , thanks for responding, the question i have though is not mentioned in the manual or quick start

In fact, there's actually two questions, the first question is what is powered by each psu in dual psu mode (psu(1) and psu(2)), it seems they may both be providing power to the cpu to distribute the load on each psu, but its not mentioned anywhere

Second question is, which psu (psu(1) or psu(2)) should be powering the pci devices? or can they both power pci devices? in general you want to use the same psu to power both the pci port and the pci device, because its possible that each psu is on a different phase (which they are in my case), but maybe it doesn't matter with this motherboard, and either psu(1) or psu(2) can power the pci devices.

For more details, this is what i'm looking at right now:
2x 1600w (constant load) psu's (1800w peak)

1x 7995wx cpu (pulling over 1000w at times)

motherboard/peripherals (400w)

nvidia 4090 (550w)

amd 7900xtx (500w)

asus hyper m.2 pci storage (rounding up to 100w)

I did talk with asus's support team, and after a few iterations they seem to have realized my question is not about hooking up the motherboard (this is specified how to do in the manual, so i do know how to do this), they assured me that either psu can be used to power the pci devices without issue. they didn't really give more information than that though so i'm still a little worried about doing it, but this is how i am going to plan to hook things up, let me know if this is wrong:

2x psus to motherboard as mentioned in manual

psu(1) powers motherboard, asus hyper m2 storage, amd 7900xtx
psu(2) powers motherboard and nvidia 4090

So now, if only the first or second psu powers the cpu, this will be an issue, but i'm under the assumption that the cpu will be powered by both psus, so in that case we can assume psu load would look something like this:

psu(1) = cpu(500w), motherboard(200w), amd gpu(500w), asus hyper m2 (100w) = 1300w

psu(2) = cpu(500w), motherboard(200w), nvidia gpu (550w) = 1250w

but if only one psu powers the cpu, then i will have to be sure to hook up pci devices to the psu that is NOT powering the cpu, which is why the question is what exactly does each psu power?

even though asus support did respond and assure i can hook up either psu to the pci devices, i felt that after a couple days of communicating there was maybe a bit of language barrier so i'm not super convinced they fully understood WHY i'm asking WHICH psu should be powering the pci devices. I will be hooking things up in the way i mentioned (one gpu per psu basically) unless someone with more information tells me not to do it that way and instead power both pci devices from one psu. Really wish their manual was more clear and detailed about the dual psu setup