With Nvidia's 12-pin connector being essentially merged 2 8-pin connectors, this gives the board a total of 375W of power (150 + 150 from 2 8-pins, and 75 from PCIe slot).
Other vendors have a variants with 2 8-pins and 3 8-pins. Which will give the board 375W and 525W respectively.
Owning a Palit RTX 3090 GamingPro with 2 8-pin, i am seeing the power limit on the card, and total consumption of roughly 360-375W, which also lands the clocks of the GPU around 1500-1750Mhz. That means that the GPU is always limited by the power given to it.
So the question is, is that a poor choice of going with 2 8-pins or there is some logic behind it? (Some people keep saying that new PSUs able to deliver more than 150W through single PCIe 8-pin)
I am running Corsair AX1200i from 2012, don't get me wrong, still an amazing piece of hardware.
2 Answers
Indeed many PSUs are able to deliver over 150 W to a single 8-pin connector. Some are even designed with just a single 12V rail (or can be configured to a single-rail mode in case of Corsair), meaning that they can support their full 12V load on any single cable.
The limitation is actually in the connector and cabling. An 8-pin is rated for 150 W and a 6-pin for 75 W. You could pull more than that from them, but that's a fire hazard. The device (in this case the video card) is responsible for managing its current draw and keeping it within design limits.
The numbers you and @harrymc have provided suggest that 3090 is operating just under the limit. It shouldn't exceed it though. Its built-in power management circuitry should keep it under the designed power limit.
On a side note, switching your PSU to single rail mode is not the best idea. Multiple low-power rails make it harder to overload cables and have the additional advantage of protection circuitry tripping earlier in case of a shorted component.
3The review Palit GeForce RTX 3090 GamingPRO OC review - Hardware setup | Power consumption sees a maximal gaming power consumption of 365W, so two 8-pins are sufficient (barely).
NVIDIA itself is more optimistic and claims the GeForce RTX 3090 only needs 350W.
Your computer will need a minimum of a 750W PSU to power the card along with everything else in your machine. Aside from the PSU itself, users need "two dedicated PCIe 8-pin power cables coming separately from the PSU".
The Founders Edition graphics cards from NVIDIA will include a 12-pin to dual 8-pin adapter, but cards from other companies aren’t expected to include the adapter. NVIDIA itself states that 12-pin power is sufficient for the RTX 3090.
