Specs Dictionary

A glossary of power supply terminology (PSU) that aims to define the most important parts of PSU technology.

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Glossaries

Term Definition
80 Plus

80 Plus is a certification of efficiency of the AC to DC conversion within a PSU. 80 Plus Certification does not mean a power supply will be 80%+ efficient 100% of the time; in fact, the 80 Plus certification only requires certain levels of efficiency at certain load levels. We have embedded a table below.

Author: Michael Kerns
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Continuous Power

Continuous power is generally referred to as the Maximum Power (Watts) a PSU can output safely continuously. Some power supplies may be able to output 800 Watts safely for a moment, but can only provide 600 Watts of continuous power. Most of the time the labeled wattage is continuous power.

Author: Michael Kerns
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Maximum Power (Watts)

Simply enough, the maximum power listed for a PSU is its maximum combined output wattage that the device is able to spit from all rails in ideal circumstances. Efficiency comes into play here, but we'll talk about that in more in the 80 Plus definition. Many users grossly over-estimate the required size of a gaming power supply, so we always suggest running your components through a power supply calculator first (though they also over-estimate, in general).

Author: Patrick Stone & Michael Kerns
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Modular Cables

Fully- and semi-modular PSUs allow for cables to be easily detached and stored. Fully-modular PSUs allow for every cable to be taken off, whereas semi-modular PSUs have cables that must be used, like the 24-pin cable, permanently attached. This allows for less clutter from unneeded cables, which can help airflow and aesthetics of a PC.

Author: Michael Kerns
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Overcurrent Protection

Overcurrent protection (OCP) is a circuit that prevents any wire or trace in a power supply from supplying more amps than its certified amount.

Author: Michael Kerns
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Overload Protection

Overload protection (OP) allows the PSU to detect when the power load exceeds its current rating, and then enforces a shutdown in order to prevent damage to itself.

Author: Michael Kerns
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Overtemperature Protection

Overtemperature protection (OTP) is straight-forward: OTP shuts down the PSU once it reaches a manufacturer-defined temperature that is deemed dangerous. This is due to temperature tolerances of the components in the PSU, padded further by the fact that as temperature increases, PSU efficiency, voltage regulation, and voltage ripple are negatively impacted.

Author: Michael Kerns
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Overvoltage Protection

Overvoltage protection (OVP) ensures that the PSU is providing the correct voltage levels to the PC. If the voltage on any rail becomes too high, OVP will shut the PSU down in order to prevent damage to any parts; too much voltage to a component can damage or destroy the component, which is the reason ESD is a concern when building systems.

Author: Patrick Stone & Michael Kerns
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Power Factor Correction

Power Factor Correction (PFC) comes in two flavors: Active and passive. Less expensive PSUs skip this altogether, simply not listing it or listing it as "no," in the case of Newegg. Some power that is being pulled from your outlet never makes it to the computer due to various reasons - heat, inefficiency, and the general rule that there is never 100% efficient energy conversion or transfer. PFC increases the amount of power that makes it to your rig in a few different ways, making your PSU more efficient.

Author: Patrick Stone
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PSU

"PSU" stands for Power Supply Unit, and is the part of a PC that transforms AC electricity to DC electricity so it is usable in a computer.

Author: Steve Burke
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PSU Form Factor

These standards define everything from the size and shape of the PSU to its electrical requirements and output. Power supply form factors have been standardized in order to increase compatibility. ATX PS/2 is by far the most popular form factor, and will fit in the vast majority of cases. ATX PS/3 is a compatible with PS/2, but is slightly shorter in depth. ATX PS/3 PSUs are less common and used more in smaller cases such as mATX cases. SFX PSUs are used primarily in small mITX cases since they are smaller than ATX PS/2 PSUs in all dimensions, but adapter brackets can be installed for compatibility with ATX PS/2 cases. Server PSU form factors exist, but are very rarely used in consumer applications. The chart below shows the dimensions for power supply form factors.

Author: Michael Kerns
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Rails (PSU)

In a PC, different components use different voltage levels, and so a power supply must take the electricity from the wall and split it into 12v, 5v, and 3.3v power. A rail is simple a wire/path inside the PSU that carries electricity of a certain voltage. The 12v rail provides power for GPUs and CPUs, generally the two most power-hungry components. It should be noted that a 12v rail can be split into multiple 12v rails, in which case two 12v rails would provide half the wattage of the combined 12v capacity.

Author: Patrick Stone & Michael Kerns
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Short Circuit Protection

Short circuit protection (SCP) is pretty self-explanatory at the top-level. Short circuit protection detects for short circuits (such as those caused by direct metal contact) and guards against those short circuits from harming the power supply or connected parts.

Author: Michael Kerns
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Undervoltage Protection

Undervoltage protection (UVP) is very similar to Overvoltage Protection in concept, just flipped. UVP shuts the PSU off if the voltage the PSU is providing to the PC drops below accepted values, and was a source for concern when ultra high-efficiency CPUs began shipping (like Haswell chips, which idled below 1W in some cases). It should be noted that like OVP, accepted values for undervoltage protection do vary from PSU to PSU.

Author: Michael Kerns
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Uninterruptible Power Supply

An uninterruptible power supply (UPS) is a separate, external battery backup that kicks-in if the power surges or goes out for a short amount of time, and also helps protect against power surges and spikes from the wall. A UPS allows for one to save their work and safely shut off their PC in the case of a power outage.

Author: Michael Kerns
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