Jamie chose an unit. Why not 750W? Because 850W gave room for future upgrades (more drives, RGB, or a hungrier GPU) and kept the PSU in its most efficient load range (40–60% during gaming, not near 80–90%).

“But it’ll never run everything at 100% simultaneously,” Jamie thought. Still, power spikes—especially on the GPU—can trip a weaker PSU.

For stability and efficiency, Jamie knew to add 20–30% headroom: 639W × 1.25 ≈

Jamie added them up: 253 + 285 + 50 + 10 + 10 + 15 + 6 + 10 = peak theoretical load.

The PC booted perfectly. Under full load (gaming + streaming), a watt-meter at the wall showed actual draw—translating to ~460–500W from the PSU after efficiency losses. The 850W unit’s fan barely spun up.

“Don’t just guess,” Jamie muttered, remembering a friend’s horror story about a cheap 500W PSU that took a motherboard with it. “Time to do this right.”