NVIDIA's GeForce RTX 5090 and RTX 5080 Power Compatibility Comparison
NVIDIA's top-of-the-line GeForce RTX 5090 has shown flexibility in power compatibility, while its counterpart, the RTX 5080, has struggled with stricter requirements. Recent tests conducted by German tech outlet ComputerBase have revealed that the RTX 5090 can function with just three 8-pin PCI power connectors instead of the recommended four, although there is a slight performance trade-off. On the other hand, the RTX 5080 fails to boot when using only two 8-pin connectors.
The RTX 5090, with a default TDP of 575 W, officially requires a 600 W 12V-2×6 connector or an adapter with four 8-pin PCI cables. However, tests on the ASUS ROG RTX 5090 Astral and Zotac RTX 5090 Solid have shown that the GPU can still boot with three 8-pin cables, limiting its TDP to 450 W, which matches the 150 W-per-cable specification. Performance losses are minimal, with benchmarks indicating a 5% decrease in average FPS at 450 W compared to full power.
On the other hand, the RTX 5080's 360 W TDP is less forgiving. Attempts to run the Founders Edition and Zotac RTX 5080 AMP Extreme Infinity with two 8-pin connectors (300 W total) resulted in failure, with the screen remaining blank and the card failing to initialize. Unlike the RTX 5090, NVIDIA's firmware for the RTX 5080 does not seem to have a lower power-limit threshold, meaning users must strictly adhere to using three 8-pin or 12V-2×6 power connectors.
While the RTX 5090 provides flexibility for users upgrading from older systems, the limitations of the RTX 5080 may be frustrating for owners with less powerful power supplies. The 5% performance penalty at 450 W for the RTX 5090 may be a reasonable trade-off to avoid costly PSU upgrades, but RTX 5080 users do not have that option. Ensuring power supply compatibility is crucial, as underpowered setups can lead to instability or hardware damage. When you have a GPU that costs over $2000, it is essential to power it properly.
This experiment serves more as a "for science" type of run to understand the power compatibility of these GPUs.

