Discussion Wattage tested: i9-13900k/RTX 4090/lots of fans ("Can you run this system with 750w PSU")


Aug 1, 2013
This is the worst case scenario with Unigine Heaven running at 4k, with Aida64 stress test running with Stress CPU/FPU/Cache selected along that Unigine Heaven running full screen. AND HWinfo64 running in the background

You will never load the system as so, as you are not supposed to run 2 benchmarks at the same time, but I did so to see max wattage in that scenario.
It runs stable by the way, until I try to open MS Paint or GPU-Z after, then I get the restart.

Wattage is rated with a meter at the wall.
4K DSR setting in NVIDIA control panel

Power supply: EVGA PQ 1000w. Manufactured by FSP. Platinum level.

Intel i9-13900k P-Cores 5.4ghz, E-cores 4.4ghz
239 average watt CPU
246.044 watt max CPU
RTX 4090 Gigabyte Gaming OC (with only 3 PCIE plugs plugged in)
290-300 watts in Unigine Heaven Ultra 4k
Hovers around 380 watts in games such as Red Dead Redemption at 1440p
Undervolted to 0.970v at 2820 mhz, can hover closer to 2805 in benchmarks such as Heaven, but will be 2820 in actual games.

Saw really strange spikes to 462 watts with 4 cables connected to GPU, and fans racing up, with random black screen.

My speculation is that when you have 4 PCIE cables into a 4 cable 12VHPWR splitter, it actually draws more than 600w on the spike from GPU alone, or forcing the doubling effect (that some report) of up to 1200w or nearly so. (Can't test this). Which trips the GPU/PSU breaker and causes complete black screen with GPU fans going at 100%.

After connecting only 3 cables to 12VHPWR 4 cable splitter = no issues.

10 Noctua NF-A12x25 case fans
2 Noctua NF-A12x25 on CPU cooler
1 PCIE x1 Firewire card
1 PCIE x4 Thunderbolt Card
3 NVME drives (M.2)
3 SSD drives (SATA)
3 USB devices plugged into the system at all times. Mouse. Keyboard. Audio Interface.

Total wattage for the whole system is 773.0 watts.
So, with power spikes in 4090 at default settings with no undervolt and stock power limit, you will most definitely will trip the breaker of the PSU, and cause immediate shut down.

Most PSUs allow some extra wattage on the 750 PSU, but far from what is enough, if my 1000watt gets tripped. I get about 250 extra watt protection on the spike by the way. Allowing me to draw 1200+ watts if system requires.

Don't put 750 watt PSU in such a system
Even in the case where I undervolted CPU, GPU, I will still trip my 750 watt power supply.

When speaking to EVGA tech, I was speaking my mind out loud, and I asked him if he knows why it happens. Then I said that I speculate that 150 watts at each PCIE plug ends up as 600 watts for total of 4, and when you have a power spike that can double the wattage usage on 4090, it brings up your power consumption to 1200 watts at worst case scenario. That spike trip my power supply, because even though I can probably draw 1250 or so with my 1000w rated PSU, having other stuff in the system easily brings it up past the limit.

Then EVGA PSU trips the breaker, "gently" locks the system without frying components, GPU begins to spin fans uncontrollably, because it doesn't see PCIE plugs at all. Similar to plugging GPU without cables into PCIE slot. The fans will go crazy.

By having 3 cables plugged in, instead of 4, I have zero black screens, or weird fan speed up with black screen. Because 3 plugs would equate at 450 watt maximum draw. So that's 900 watt at worst if the spike doubles the usage (even for split second).
EVGA tech actually agreed on that theory. Considering how helpful EVGA has been with me, I would say he knows what he is talking about. Perhaps my theory is correct.

This is my speculation of why companies suggest minimum of 1200 watt PSU, or even greater.
Because those voltage spikes on 4090 cause this nonsense. I personally do not see the difference in fps between 3 and 4 cables. But I do see the wattage going up to 462 during benchmarks, while with 3 cables no such thing happens.

Food for thought.