What is a PSU in a Computer – Voltages, Types & Functions

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What is a PSU in a computer?Many come across the various components of the computer like the motherboard, CPU, GPU, mouse, monitor, and many more.

The most sidelined component is the PSU or the Power Supply Unit. The most essential part of the computer. It is like the heart which pumps blood in the body of an animal or human being.

The PSU supplies current or power to the computer and its components. Without the power supply, the user will not be able to start the computer at all. The computer cannot do anything without the power supply.

Since it is electronic and needs electricity in the computer. It is supplied by the PSU. The Power Supply Unit on the computer has many functions and types.

There is AT or the Advanced Technology supply power. ATX or the Advanced Technology Extended, EPX12V, CFX12V, and many more. The laptop has batteries because of its being portable.

But also has a power supply unit that comes in a small portable thick plastic box. Which is not that more powerful than the computer supply unit used in desktop computers.

The PSU consists of many components like a fan, many colorful wires, and many more. Repairing or upgrading the PSU is not always possible and one has to keep the compatibility of the motherboard and the PSU in mind.

It also helps to convert the current coming from the switchboard which is the Alternative Current or the AC to Direct Current or DC.

Direct Current is preferred by the other components of the computer; the voltage in the power supply of the computer fluctuates from 3, 5, and 12.

They can’t go extreme below or extreme above and if it does it will cause a lot of problems. As new devices come in the market, power supplies are also being updated and becoming advanced the ATX has many latest versions used by many computers.

Therefore, the PSU is an integral part of the computer.

What is a PSU in a Computer?

What is a PSU in a Computer

The computer consists of a lot of hardware. And the Power Supply Unit or the PSU is also a part of the computer.

It is also hardware. By the name, one can understand the power supply unit of the PSU supplies power to the other parts of the computer.

It helps to convert the power which is given from the outlet into a power supply which is then used by the other parts of the computer.

The PSU is usually located at the top back of the computer. But these days the power supply is placed at the bottom of the computer case right at the back.

The outlet which is in the wall is plugged in and it is then converted from Alternating Current to Direct Current. Which is a continuous flow of power.

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Knowing the difference between the Alternating Current and the Direct Current is essential. It is an amazing work of Technology.

Which is always sidelined by the other famous components like the CPU, the motherboard, and the others.

If there is no power supply then the computer will not be able to start.

The PSU comes in many sizes, especially which can fit in most of the cases for computers.

The width and height may be the same but the length and how long it is depends on manufacturers.

Some popular power supply unit manufacturers are CORSAIR, Ultra, and even CoolMax. These come with the computer when purchased or even while customizing.

Many users are unable to see what the computer supply usually consists of because it is mostly placed at the back and in a case. It consists of a fan that transfers the air out of the computer case.

It contains three prolonged ports (male). Which is connected to the power source. One of them consists of two switches, a power switch or even a power supply voltage switch.

There are colorful wires into which they are connected to the different parts. Then it supplies power. For instance, there are wires which are connected to the fans, motherboard, GPU, and many more.

One most important component of the PSU is the fan and if it does not work then it causes a lot of problems. A power supply unit usually cannot be repaired.

Many users avoid opening the power supply unit. The rating of the power supply unit of the PSU is in terms of wattage. The more powerful the computer the more Wattage the PSU provides to the other parts of the computer.

Both the personal computers consist of the same components of the PSU. But there is the outer appearance that differs. In the desktop computer, the PSU comes in a metal box for proper protection and it becomes very heavy.

But in laptop computers, it comes in a thin plastic box they cannot be internally attached. So they are externally plugged in to make the laptop run.

Also, the power supply units are named depending on how much power it can give. The power supply unit comes with the label which informs the users about PSU’s information.

Like how much power one voltage line can give. Many electronic markets sell PSU and they have various prices for all kinds of PSU.

The user should choose the PSU according to the budget and how much power it can deliver. It also depends on the demand of the Power the Other components of the computers want.

Types of Computer Power Supply

Choosing the right power supply is important. Because if there is no power supply the computer will not work at all.

  • AT power supply

The traditional power supply or the AT power supply is also known as the Advanced Technology power supply. It is the predecessor of the ATX power supply. It is the first power supply used for computers.

Then the need for computers was raised. The AT power supply provided a wattage of 250. Which was less than the others. Therefore, the need for Advanced Technology power supply had dropped drastically.

  • ATX

ATX or the Advanced Technology Extended. These are an advanced type of power supply for computers. ATX also has a motherboard designed.

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Therefore, to match the ATX motherboard one needs to purchase an ATX power supply. It was developed in the year 1995 by the famous manufacturer Intel. It outperformed the traditional power supply.

The ATX power supply provided plus 3.3 voltage extra voltage rail. It even provides a “soft off” feature. The power supply is turned off by the software. And it is allowed by the ATX power supply.

Lastly, the ATX power supply comes with a 20 pin connector which is single. And which is the main power connector. The ATX power supply rating is below 70% and its efficiency is quite low.

  • ATX12V

The ATX12V has become very popular these days. It has outperformed the ATX power supply. The ATX12V has many variants or versions. Those versions are different from one another.

The ATX12V is an advanced power supply. And it is a bit better product than the ATX form factor. Adding a few better specifications like the extra 4oin  connectors.

It also comes with a 12V connector. The 12V connector helps deliver power to the professor exclusively. The newest version is the ATX12V version 2.4 which is used by many computers.

They consist of 24 pin connectors that come in the same size as the ATX power supply. One can use any ATX power supply motherboard with an ATX12V power supply.

But the ATX motherboard allows 20 pin connectors. There has to be a lot of space where the 24 pin connector can be used as a better alternative.

The remaining four pins are not used.  And space is an important factor here. But the ATX power supply cannot be connected to an ATX12V motherboard because of the number of pins.

12V is quite efficient and its efficiency is above 80% rate which is better than the traditional power supply AT and ATX.

The other power supply includes below:

  • There is EPS12V power supply that is used by the high end desktop computers motherboard.
  • There is a range of smaller power supplies like the SFX12V also known as Small Form Factor, CFX12V also known as Compact Form Factor, the LFX12V also known as Low Profile Form Factor and lastly TFX12V also known as Thin Form Factor. These are used in small computer cases.
  • ATX and ATX12V are both used for desktop personal computers. There is another type of computer power supply which is used in personal computers. It is called the External Power Supply. The one which is used in gaming consoles and many more. It is an external power supply which is usually large and attached to the power cable.
  • There’s always a backup for things. And there is also a backup power supply which is also known as UPS or the Uninterrupted Power Supply. It is used when the main power supply is disconnected.

Computer Power Supply Voltages                                                                        

PSU or the power supplies are used to convert the Alternating Current or AC coming from the output to Direct Current or DC which is lower. Voltages vary and it sounds very simple to understand.

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The supply comes in voltages like 3.3 volts, 5 volts, and 12 volts. These voltages do not necessarily have to be exact. But it can only vary till a certain point be it below or above.

But if it goes extreme then it may cause problems. The voltage is a product of Watts. The Power supply usually used these days are as follows:-

  • Digital circuits require 3.5 volts. The tolerance level is ± 5%. The minimum voltage it can provide is + 3.135 VDC. Whereas the minimum voltage provided is + 3.465 VDC.
  • For + 5 VDC or Voltage Direct Current, the tolerance level is again as same as ± 5%. The minimum voltage provided is + 4.750 VDC and the maximum voltage provided is + 5.250 VDC.
  • The + 5 VSB or the Voltage Standby. It is also used for digital circuits. The tolerance level is ± 5%. The minimum and the maximum voltages are + 4.750 VDC and + 5.250 VDC, respectively.
  • Voltages at tolerance are ± 10% and are the – 5 VDC. So, the maximum and minimum voltages it provides is – 4.500 VDC and – 5.500 VDC, respectively.
  • The 12 Volt Direct Current is used for disk drives and also to run the motors and the fans. The 12VDC and – 12VDC have different tolerance levels, the 12VDC can fluctuate from +11.400 VDC to +12.600 VDC and the latter fluctuates from – 10.800 VDC to – 13.200 VDC. The tolerance level is ± 5% and ± 10% respectively

Power Supply Functions

  • Without the power supply, the computer will not work. Therefore, the user will not be able to use the computer.
  • PSU or the power supply provides the other parts of the computer electrical current.
  • It helps in converting the Alternating current (AC) coming from the output or the switchboard to Direct Current (DC) which goes to the other parts of the computer.
  • The fan attached in the PSU is used to blow out the heat which is generated by the computer.
  • UPS or the Uninterruptible Power Supply helps in the power supply of the user’s computer from “surges” and “voltage drops”.


Where is the PSU located in a computer? 

Previously the PSU was located at the top, back of the computer. But, now it is located at the bottom of the computer case, at the back.     

How long does a PSU last?

It depends on how well it is handled. Usually, the PSU lasts 5-7 years. And if handled very well then it can last more. Brand and quality also depend.

What causes PSU to fail?

If the fan stops working and also due to overheating. Also, if the PSU is badly handled then it will lead to failure. Here also it depends on the quality and how well it works.


This hardware does not stop being manufactured because of the importance it holds in the world of computers. No power supply, no functioning of the computer.

Being so important. One should take proper care of the computer. And also not to fiddle with the power supply unit. It is very difficult to repair and is very dangerous to fiddle with.