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Quick Answer
850W is the absolute minimum for the RTX 4090 + i9-14900K. This power-hungry combo draws 650-750W under gaming load with transient spikes exceeding 900W. We recommend 1000W for reliable, stress-free operation with this flagship pairing.
When RTX 4090 transient spikes coincide with CPU load spikes, total system draw can momentarily exceed 850W. Quality ATX 3.0 PSUs handle brief overcurrent, but it is not ideal for long-term reliability. Running a PSU near its limit increases heat, reduces efficiency, and shortens its lifespan.
For a system that costs $5000-7000 AUD, an extra $40-60 for 1000W is trivial. You get proper headroom, peak efficiency at your actual load, and zero risk of transient-related shutdowns.
Whether you choose 850W or 1000W, an ATX 3.0 PSU is essential for the RTX 4090. The native 12VHPWR connector and improved transient handling are designed specifically for these power-hungry GPUs.
Our Verdict
850W can work but is risky for the RTX 4090 + 14900K. Spend the extra money for 1000W. On a build this expensive, do not compromise on the power supply.