What is a power supply unit (PSU) and what is it for?

What is a power supply unit (PSU) and what is it for?

A power supply is a device that converts alternating current into one or more direct currents, which feed the different circuits that are connected to it (Motherboard, HDD,…)

Types of Power Supplies

Power supplies can be divided into linear and transformed power supplies.

Linear sources: they have a simple design, which could be a little more complicated the greater the current that must be supplied, however their voltage control is not as efficient.

A transformed source, which has the same power as a linear one, will have the characteristic that it will be smaller and generally more efficient, but it will be more complex and for this reason much more susceptible to power outages.

Maintenance recommendations

It is recommended that the power supply is always kept clean. Otherwise, the dust that accumulates will not allow air to escape; and when the temperature rises,

this component could overheat and as a result make all its components suffer. It should be noted that failures that may occur in the power source can damage other elements of your computer, such as the motherboard or graphics card.

How to choose a power supply?

How to choose a power supply?

It is essential before choosing a power supply that you take into consideration some factors:

  • The power it supplies
  • Available font formats
  • Accessories that are available

As a general rule, these sources provide you with the amount of power (W) necessary for your equipment and components for a long period of time. All this without a trace of excessive overheating.

If you choose sources of less distributed brands (this does not mean that because they are less distributed they are bad) you can run the risk

that the quality of their components and powers are irregular. In the vast majority of cases they indicate that the manufacturing quality is poor.

What is the power supply for?

Power supplies use switching technology to convert alternating current (AC) to direct current (DC). To do this, it uses voltages that can be 3.3, 5 or 12 volts . Nowadays, more than 90% of the load of the computers is placed in the 12 V.

On the other hand, thanks to new technologies, the operation of power supplies is becoming more and more sophisticated .

For example, the operating system is able to send a signal to the PSU in order to tell it to turn off the computer. The same when turned on.

Turning the PC off and on, which is currently very simple to do, used to be much more tedious because the power supplies were big and heavy (the well-known transformers). Consequently, it took much longer. Today everything is more compact.

In turn, the alternating current supplied by the power supply is easy to filter and rectify , which reduces noise and voltage variations.

All this translates into four essential functions for the operation of the computer:


The coil transformer makes it possible to reduce the input voltage to the source, generating an output of 5 to 12 volts .


The rectifier bridge is in charge of ensuring that the voltage does not drop below 0 volts , in other words, that oscillations occur that can seriously damage the computer.


The signal is flattened as much as possible, thanks to one or two capacitors, which hold the current and let it pass slowly.


When the signal is already continuous and almost completely flat, the only thing left to do is stabilise .

Parts of a power supply

Currently, there are two types of power supply , whose characteristics and operation are very different. We are talking about AT and ATX devices .

The parts of a PSU AT are:

  • Ventilator.
  • mechanical switch.
  • supply connector.
  • 4-terminal MOLEX and BERG connector.
  • Conector AT.
  • Voltage selector.
  • Supply connector to other elements.

For their part, ATX power supplies have:

  • Ventilator
  • BERG and MOLEX 4-terminal connector.
  • Power connector.
  • SATA connector
  • Conector ATX.
  • Voltage selector.
  • Security switch.


Of the standard power supplies there is not much more to add because they are the ones that have the characteristics listed above.

With regard to the modular ones , they are characterised by having cables that feed the PC that can be connected according to our own needs. In other words, if for example we have a motherboard and a hard drive, we only have to put two cables . 

The main advantage of these devices is that, by having fewer cables, we improve the ventilation of the computer case.


These fonts are similar to standard fonts, except they are smaller . This makes them adapt to any type of deviceIts size is usually 125 x 100 x 63 mm and the power is significantly less than that of a normal PSU due to its limitations.


On the other hand, there are external power supplies , which although they are usually used in video game consoles, many gamers also use them in their computers.

This is due to the fact that they need a greater stability of the current because they have the device turned on for a large part of the day.

What to do if the power supply has problems?

Unfortunately, the power supply of the computer has great possibilities of suffering failures for two reasons related to its operation.First of all, we have to take into account that every time we use the PC , heat and cold enter constantly .

On the other hand, the source is the one that receives the input alternating current when the computer is turned on.

There are several signs that the device is failing. Some of the most common are: random PC reboots, fan not working, and video game slowdowns.

In any case, a quality power supply can last up to 10 years without failure (always depending on the use we give the computer, of course).

If a problem appears, the recommendation is that we do not try to fix it because it is an extremely complex device to repair.

In these cases, the best thing you can do is go to a specialised technician who will tell you if the source can be fixed or you should buy a new one.

James Hope
My name's James and throughout the long term. I have actually assembled numerous PCs for me as well as my companions. I love gaming, programming, illustrations planning and essentially whatever has to do with PCs and innovation.