Power supply efficiency is the amount of power that a power supply unit (PSU) can convert from the AC power from the outlet into DC power, which is used by your computer components.
PSUs are never 100% efficient, meaning not all the power they draw from the outlet is converted into usable power. Some of it gets lost, mainly in the form of heat. The efficiency of a PSU is the percentage of the AC input power that’s converted to DC output power.
For example, if a PSU is 80% efficient and your computer uses 400 watts, that means the PSU actually pulls around 500 watts from the wall. The other 100 watts are dissipated as heat.
A higher efficiency PSU will waste less energy as heat and will therefore require less cooling, leading to quieter operation. Moreover, it will also result in slightly lower electricity costs over the long run.
What is Power Supply Efficiency
Power supply efficiency is the ratio of output power generated by a PSU to the input power it consumes to generate the required output power. Mathematically,
Efficiency= output power/input power
Expressed in percentage, power supply efficiency gives you a tentative idea of how much AC power the PSU actually converts into DC. This way, you can know the useful power and the power that goes to waste, often in the form of heat.
The lower the power supply efficiency of your PSU, the more electricity it wastes and the more heat it generates
For instance, you have a PSU with a wattage rating of 1000W and 50% efficiency at a full load. Based on the above formula, here’s the calculation of how much power it will draw from the wall socket to provide the output of 1000W:
50% = 1000 / input power
Input power = 1000/50%
Input power = 2000WThis means that the PSU draws 2000W and supplies 1000W. The remaining 1000W does not make it to the PC components.
However, there are almost no PSUs that are this inefficient. Most of the PSUs these days provide efficiency anywhere between 70% to 80%. But there are also PSUs that provide an efficiency of 90% or higher.
This is where the 80 PLUS certification comes in and standardizes the efficiency rating.
Power Supply Efficiency Rating
PSU manufacturers generally rate their power supply units with the “80 PLUS voluntary certificate program.” Introduced back in 2004, the 80 PLUS rating certifies that the PSU can maintain a minimum of 80% efficiency at varying loads.
To be more precise, PSU has to maintain an efficiency of 80% when it is generating either 20%, 50%, or 100% power of the rated output power.
For instance, if you have an 80 PLUS certified PSU of 600W with an average efficiency of 80%,
| Power Drawn from Wall Socket | Power Output | Power Wasted | |
| At 100% load | 750W | 600W | 150W |
| At 50% load | 375W | 300W | 75W |
| At 20% load | 150W | 120W | 30W |
80 PLUS certification is further categorized into six different levels, namely 80 PLUS “White”, Bronze, Silver, Gold, Platinum, and Titanium.
Here’s a quick overview of the power supply efficiency corresponding to the 80 PLUS certification levels.
| White | Bronze | Silver | Gold | Platinum | Titanium | |
| 10% Load | – | – | – | – | – | 90% |
| 20% Load | 80% | 82% | 85% | 87% | 90% | 92% |
| 50% Load | 80% | 85% | 88% | 90% | 92% | 94% |
| 100% Load | 80% | 82% | 85% | 87% | 89% | 90% |
As you go up in the hierarchy list, the quality of the electronic components (like capacitors, rectifiers, and chokes) used in the PSU keeps on improving. As such, the PSU certified with a higher level of 80 PLUS rating is expected to provide better efficiency than one on the lower levels.
Choosing an Efficient Power Supply Unit
It is always a better option to get an 80 PLUS certified PSU rather than one with no certification. Not only are they reliable and power efficient, but they are also tested for safety and optimal performance.
Generally, you can go with the Bronze or Silver variant if you are using it with a budget build. For instance, a PC for your home or office use.
Similarly, the Gold variant might be a suitable option if you are planning to use it with a high-performance systems like your gaming setup. It offers higher efficiency than the Bronze and Silver variants with improved cooling and quieter fans.
Having said that, it does not necessarily mean that the Bronze and Silver variants are inefficient. Choosing the efficiency rating for a PSU depends on your budget, efficiency requirement, and setup.
For high-end PCs or a server setup, you can even go for an 80 PLUS Platinum or 80 PLUS Titanium variant. However, you should again take your budget and efficiency requirements into consideration.
If you are stuck between choosing Gold or Platinum, you can quickly go through our Gold vs Platinum power supply guide to know more about them.
From the above curve, we can compare the efficiency of each 80 PLUS-certified PSUs at varying loads.
At 20% load, the efficiency for each of them seems to be minimum. As the load rises and reaches around 50%, the efficiency is at its maximum. However, when the load further rises and nears 100%, the efficiency tends to be lower and gradually sets to the lowest.
How to Check Power Efficiency Certification
Most PSUs today have an 80 PLUS certification label mentioning their power efficiency. You can easily check the rating by looking at the label on the PSU itself. Besides, you can also check the specifications on the manufacturer’s website or from the 80 PLUS authority.
There are also other authorities like CYBENETICS that provide efficiency ratings along with the noise level rating for PSUs. Unlike the 80 PLUS rating, CYBENETICS has a different efficiency rating for each level of certification. You can visit the CYBENETICS official to learn more about it.
Effect of PSU Efficiency on Power Bill
Higher-efficiency PSUs often have high-quality builds that reduce electrical noise and ripple, leading to more stable performance. Although more costly than PSUs with lower efficiency, high-efficiency PSUs draw less power from the grid and are also helpful in reducing your power bill.
Here’s a quick power bill comparison for two 1000W PSUs, one with an efficiency of 80% and another one with 90%.
| Rated Power Output | PSU Efficiency | Actual Power Consumption | Electricity Rate for kW/h | Total Cost Per Hour | Monthly Cost (on 8 hours daily use) | |
| PSU 1 | 1000W | 80% | 1250W | $0.15 | $0.187 | $43.2 |
| PSU 2 | 1000W | 90% | 1111W | $0.15 | $0.166 | $39.9 |
With that, I hope you are also now aware of the effect of PSU efficiency on your power bill. So, it is also recommended to go for a high-efficient PSU if you seek reduced operating costs.