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A power supply unit (PSU) is a device that converts alternating current (AC) from the wall outlet into direct current (DC) that is suitable for the internal components of a computer.
A PSU provides different voltages and currents to the motherboard, CPU, GPU, storage devices, fans, and other peripherals. A PSU also regulates the voltage and protects the components from power surges or fluctuations.
The rating system for PSUs is based on the 80 Plus certification program, which measures the efficiency and reliability of a PSU. Efficiency is the ratio of the output power to the input power, and it indicates how much power is wasted as heat. Reliability is the ability of a PSU to maintain stable voltages and currents under different loads and temperatures.
The 80 Plus certification program has six levels of ratings: 80 Plus (or White), Bronze, Silver, Gold, Platinum, and Titanium. Each level has a minimum efficiency requirement at 20%, 50%, and 100% load, as well as a minimum power factor correction (PFC) value.
Power Factor Correction or "PFC", is a measure of how well a PSU aligns the input voltage and current waves, and it affects the stability and quality of the power supply.
The higher the rating level, the more efficient and reliable the PSU is, but also the more expensive it is.
A higher-rated PSU can save energy and reduce heat and noise, but it may not be necessary for every PC user.
The choice of a PSU rating depends on factors such as the power consumption of the PC components, the electricity cost, the ambient temperature, and the personal preference.
| Rating | 20% Load | 50% Load | 100% Load | PFC |
|---|---|---|---|---|
| 80 Plus (White) | 80% | 80% | 80% | 0.9 |
| Bronze | 82% | 85% | 82% | 0.9 |
| Silver | 85% | 88% | 85% | 0.9 |
| Gold | 87% | 90% | 87% | 0.9 |
| Platinum | 90% | 92% | 89% | 0.95 |
ATX: This is the standard form factor for most desktop PCs. It has a single 24-pin main power connector for the motherboard, and it supports features such as soft-off (allowing software to turn off the PSU) and standby power (providing power to some components even when the PC is off). ATX PSUs have dimensions of about 150mm x 86mm x 140mm (W x H x D).
SFX: This is a smaller form factor for compact PCs, such as mini-ITX or micro-ATX builds. It has similar features to ATX PSUs, but it has a smaller main power connector (20-pin or 24-pin) and smaller dimensions of about 125mm x 63mm x 100mm (W x H x D). Some SFX PSUs come with adapters to fit in ATX cases.
TFX: This is another small form factor for slim PCs, such as home theater PCs or all-in-one PCs. It has a longer and thinner shape than SFX PSUs, with dimensions of about 85mm x 65mm x 175mm (W x H x D). It also has a smaller main power connector (20-pin or 24-pin) and lower wattage than SFX PSUs.
Flex ATX: This is a very small form factor for ultra-compact PCs, such as mini-ITX or thin clients. It has a similar shape to TFX PSUs, but with even smaller dimensions of about 81mm x 40mm x 150mm (W x H x D). It has a small main power connector (20-pin or 24-pin) and very low wattage than TFX PSUs.
There are other less common form factors for PSUs, such as EPS (for servers or workstations), CFX (for slim desktops), LFX (for low-profile desktops), or AT (for older PCs). However, these are not widely used in modern PCs.