Is 850W enough for an RTX 5080 + Core i9-14900K? (measured, not TDP)

Yes — 850 W handles this combination with room to spare.

noteSustained load: 653 W (Core i9-14900K 282 W measured peak + GeForce RTX 5080 296 W measured gaming + 75 W rest of system) = 77% of a 850 W unit.
goodSustained load is 77% of the unit's rating, and even the worst measured spike total (780 W) stays under 850 W.
noteSpike check: 282 W CPU + 423 W GPU spike + 75 W = 780 W momentary worst case — within the unit's rating.

The math, with sources

GPU sustained draw: 296 W — GeForce RTX 5080 measured while gaming (TechPowerUp — GeForce RTX 5050 review, Power Consumption charts (July 2025 test suite)) — its rated board power is 360 W.
GPU transient spikes: 423 W — GeForce RTX 5080 spikes to ~423 W for milliseconds (TechPowerUp — GeForce RTX 5050 review, Power Consumption charts (July 2025 test suite)). Spikes trip older PSUs that averages never show.
CPU peak draw: 282 W — Core i9-14900K measured under heavy all-core load (TechPowerUp — Core i9-14900K review, multi-threaded power chart (Blender, CPU-only)). Games draw less, but renders, encodes and shader compiles hit this.
Rest of the system: 75 W — Motherboard, RAM, drives, fans and USB devices — a fixed allowance.
Sustained total: 653 W — 282 + 296 + 75 = 653 W of steady load.
With 15% headroom: 751 W — Sustained x 1.15 — margin for capacitor aging, heat, and staying near the efficiency sweet spot. (The sustained figure is already conservative: CPU all-core peak and GPU gaming peak rarely coincide.)
Spike check: 780 W — CPU peak + GPU spike + rest = 780 W for milliseconds. The recommendation also covers this outright, so even a pre-ATX-3.0 unit is not spike-tripped.
Recommended: 850 W — The smallest standard size covering both 751 W (sustained + headroom) and 780 W (spike total).

AFFILIATE_SLOT: tested 850W ATX 3.x unit picks will be listed here. No links yet — added only once real recommendations exist.