Experiencing Black Screen Crashes with Multiple GPUs – Any Solutions?

Hey everyone,

I've run into a frustrating issue with my new PC build and could really use some advice. For the past couple of weeks, I've been dealing with my GPU crashing out during gameplay, specifically while playing Baldur's Gate 3 and Warhammer 40,000: Rogue Trader.

While the GPU performed perfectly in 3DMark stress tests (both Steel Nomad and Time Spy at 4K), the crashes happen almost immediately during gaming and can be replicated with the OCCT power stress test.

When the crash occurs, I'm left with a black screen, but the system keeps going—I can still hear Discord rings in the background. The only fix is a hard reset of the PC.

Here are my specs:
- **Motherboard:** X870M AORUS ELITE WIFI7
- **CPU:** Ryzen 9 9950X3D
- **CPU Cooler:** Lian Li Galahad II Trinity 360mm
- **Primary GPU:** Gigabyte Gaming OC GeForce RTX 5090
- **Test GPU:** Gigabyte Aorus Xtreme GeForce RTX 3080
- **PSU:** Corsair SF1000
- **RAM:** G.Skill Trident Z5 (6000, 32GBx2)
- **Case:** Lian Li m3-atx (optimized airflow)
- **Monitors:** MSI OLED 4K 240HZ & AOC 1080p 75HZ (both via DisplayPort)

The problem has evolved to show live kernel events and timeout errors, indicating something's misfiring either with the graphics cards or the PSU. I did a thorough check on the system, including RAM tests and stress tests on the CPU, all of which came back clear.

I reset everything to stock settings to nudge out potential overclocking issues, cleanly reinstalled drivers, and even got an RMA on my 5090, but the crashes persisted with the borrowed 3080. I suspect there's a deeper issue, possibly with power handling when the CPU and GPU are under load together. My PSU worked fine in a lower-power setup but seems to struggle here.

Has anyone successfully run a configuration like mine without having to dial back power limits? I'm trying to figure out if I'm just facing transient power issues or if I might have a fault somewhere. Any advice or tests I might have missed would be greatly appreciated!