okay funny he should ask. as I have 2x 3090 with 1x 3070
and I think it is a seasonic focus. 850 watt
my 3090 gear use 3 jacks each and my 3070 uses 2 jacks.
so 1 cable and 1/2 cable to one 3090
and 1 cable + 1/2 cable to second 3090
and 1 cable to 3070
I pull 259 + 259 + 119
the full rig is 677
let me check if it is the 1000 watt model.
it is the 1000 watt model
I have 8 pcie plugs across 4 cables
now if you are really slick on this psu you can adapt the molex cables a pcie cable.
https://www.amazon.com/Cable-Matters-2-Pack-8-Pin-Inches/dp/B01DV1Z428/ref=sr_1_3?dchild=1&keywords=molex+to+pcie&qid=1617202991&sr=8-3this would allow
9 pcie plugs across 4 pcie cables and 2 separate molex cables.
Still I pull 677 and my kill a watt says 714 watts on my 1000 watt focus with 2x 3090 and 1x 3070. and my seasonic feels hot to the touch.
So I do not think the op can safely run 2x 3090 and 1 x 3080 on the 850 watt model
as I am having a hot 1000 watt with 2x 3090 and 1x 3070