Between the wall outlet and your CPU and GPU sits the power supply unit (PSU), and it is not a perfect pipe. Some of the electricity it draws is lost as heat during the conversion from AC mains to the DC voltages your components use. That loss is the PSU's inefficiency, and for a rig running long hours it adds up.
What 80 PLUS means
The 80 PLUS scheme certifies how efficient a PSU is at converting power. The tiers, from lowest to highest, are roughly:
- 80 PLUS White - about 80% efficient.
- Bronze - about 82-85%.
- Gold - about 87-90%.
- Platinum / Titanium - about 90-94%.
An 85% efficient PSU delivering 400W to your components is actually pulling roughly 470W from the wall - the missing 70W is waste heat radiating off the PSU itself.
The efficiency sweet spot
PSUs are most efficient at around 50% of their rated load and least efficient at very low load. A 1000W PSU running a 250W rig sits in an inefficient part of its curve, wasting more proportionally than a right-sized 500W unit would. Bigger is not better for efficiency - matching the PSU to the rig is.
Doing the waste maths
Say your components need 400W and you run 24/7 at $0.16/kWh:
- At 80% efficiency, wall draw is 500W. Monthly cost ~$58.
- At 90% efficiency, wall draw is 444W. Monthly cost ~$51.
That is roughly $7/month, or $84/year, saved purely by the PSU being better - while your components do identical work and earn identical MLRT.
When an upgrade pays back
If you already own a decent Bronze or Gold unit, swapping it is rarely worth it on efficiency alone. But if you are buying a new PSU anyway, or running an old, no-name unit of unknown efficiency, choosing Gold over the cheapest option is a small premium that quietly pays for itself over a couple of years of mining hours.
Bonus: less waste heat
A more efficient PSU also dumps less heat into the room and into the case, which means lower temperatures, quieter fans, and - in summer - slightly less load on any air conditioning. The efficiency gain shows up twice.