Is 550W enough for an Arc B580 + Ryzen 5 9600X? (measured, not TDP)

Yes — 550 W handles this combination with room to spare.

noteSustained load: 320 W (Ryzen 5 9600X 80 W measured peak + Arc B580 165 W measured gaming + 75 W rest of system) = 58% of a 550 W unit.
goodSustained load is 58% of the unit's rating, and even the worst measured spike total (393 W) stays under 550 W.
noteSpike check: 80 W CPU + 238 W GPU spike + 75 W = 393 W momentary worst case — within the unit's rating.

The math, with sources

GPU sustained draw: 165 W — Arc B580 measured while gaming (TechPowerUp — GeForce RTX 5050 review, Power Consumption charts (July 2025 test suite)) — its rated board power is 190 W.
GPU transient spikes: 238 W — Arc B580 spikes to ~238 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: 80 W — Ryzen 5 9600X measured under heavy all-core load (TechPowerUp — Ryzen 5 9600X 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: 320 W — 80 + 165 + 75 = 320 W of steady load.
With 15% headroom: 368 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: 393 W — CPU peak + GPU spike + rest = 393 W for milliseconds. The recommendation also covers this outright, so even a pre-ATX-3.0 unit is not spike-tripped.
Recommended: 450 W — The smallest standard size covering both 368 W (sustained + headroom) and 393 W (spike total).

AFFILIATE_SLOT: tested 450W ATX 3.x unit picks will be listed here. No links yet — added only once real recommendations exist.