A power supply that is too small does not always fail loudly. It shuts down under transient spikes, ramps its fan or causes crashes that look like a driver bug.
Read the **12 V amperage** on the label, add the realistic **GPU and CPU** draw plus 100 W, and compare with the unit's rating. Measure at the wall to see what the machine really pulls.
The number that matters is the 12 V rail in amps. Multiply it by 12 for the wattage available to the CPU and GPU; the rest of the total is shared with drives and fans.
Add the GPU's board power and the CPU's package power under load, then 100 W for board, drives and fans. Peak numbers from reviews are the useful ones, not the TDP.
GPU 320 W + CPU 150 W + 100 W = 570 WModern graphics cards spike well above their average for milliseconds. A unit at 80 % of the estimate rides those spikes; one at 100 % trips its protection and reboots the PC.
A plug-in meter shows the true consumption of the whole system. Under a game and a stress test the number should stay below the PSU rating, adjusted for its efficiency.
A card needing three 8-pin connectors wants three separate cables from the unit. Daisy-chaining two plugs on one cable pushes the whole load through one set of wires.
Shutdowns under load, a fan that screams at idle, coil whine that changes with frame rate and crashes that no driver fixes all point at the power path before anything else.
Protection trips on a transient spike. Check the 12 V capacity and the cable layout before you blame the driver.
Heat, not power. The PSU is drawing its own exhaust air; give it a clear intake path.
The load is not what you think. Run a combined CPU and GPU stress test and read the meter again.
Some units ramp on temperature, not load. Check the exhaust temperature and the dust filter before replacing anything.
No. Efficiency peaks in a band, and an oversized unit idles far below it. Size to the real draw plus headroom.
For a modern high-end card it removes the adapter question. For a mid-range build a good ATX 2.x unit is fine.
Nothing in this guide changes software. If you replaced cables, put the original layout back before returning the unit.
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