A common instinct when building a mining rig is to buy the biggest power supply you can afford, on the theory that more headroom is safer. For efficiency, that instinct is backwards. A wildly oversized PSU running a modest load wastes more electricity and runs no quieter than a correctly sized one. Right-sizing is a small decision that pays back every hour the rig runs.
The efficiency curve
Power supplies are not equally efficient at all loads. They are most efficient at roughly half their rated capacity and least efficient at very low load. A 1,000W unit asked to deliver 250W is operating down in the inefficient part of its curve, converting a larger share of input power to waste heat than a 500W unit delivering the same 250W would. The components do identical work either way; the oversized supply just spills more energy on the floor.
How to size it
- Measure or estimate your components' real draw. A single-GPU Malairte rig is often 250-450W at the wall, including PSU losses.
- Work back to the DC load the components need - somewhat less than the wall figure, since the wall figure already includes PSU inefficiency.
- Choose a PSU whose rating puts your typical load near the 50% sweet spot. For a 300W component load, a 500-600W unit sits comfortably in its efficient band with sensible headroom.
The headroom you actually need
Headroom matters for transient spikes and for not running a supply at its absolute limit, but 20-40% over your peak draw is plenty. Tripling the rating "to be safe" buys nothing useful and pushes you off the efficient part of the curve. A right-sized 80 PLUS Gold unit beats an oversized cheaper one on running cost almost every time.
Quieter and cooler, too
A right-sized, efficient PSU produces less waste heat, so its own fan spins slower and the case stays cooler. That means a quieter rig you can comfortably run in a home office, and slightly less heat dumped into the room - a small bonus in summer. The efficiency win shows up as lower bills, lower temperatures, and lower noise simultaneously.
A grounded buying rule
When you buy, pick the highest 80 PLUS tier you can justify and a wattage that puts your real load near half the rating. That single pair of choices captures almost all the available efficiency without overspending on capacity you will never use. It is the kind of quiet, disciplined decision that defines a well-built home rig.