How To Choose A Power Supply (PSU) For Your PC?

If all goes well, you may not even pay attention to the PSU, but when failures start to appear, we all remember it. That is why it is important to know how to choose a suitable power supply for your computer. In this article, we tell you everything you should take into account when choosing the right one.

Power output: how much do you need?

Although throughout this article we will see some key factors when choosing a power supply, the truth is that the most important is surely power. You don’t have to read reviews about how much power you need as you can use BeQuiet’s PSU power calculator.

Let’s give an example. You want to assemble your computer based on Ryzen 9 5950X and an Nvidia RTX 3080. To do this, you must go to the calculator and select the components that you have used for your assembly.

After selecting the components, your preferences and the option to choose the price range should appear.

You have to keep in mind that this calculator already makes an overestimated calculation, so it is not necessary to purchase a power greater than the recommended one.

BeQuiet's PSU power calculator
BeQuiet’s PSU power calculator

Power supply wiring

Power supply wiring
Power supply wiring

When you buy a power supply, you find a tangle of cables very similar to the one in the photo. One end of the cable connects to the device to be powered, and the other to the power source.

Most common connectors and uses

Next, we are going to see what are the most common connectors and their main uses.

24-pin power connector to power the motherboard

This type of 24-pin cable powers the entire motherboard, which also includes RAM, PCIe devices, expansion cards, and controllers… This connector supplies power at 3 different voltages (3.3, 5, and 12 V)

8-pin (4+4) ATX +12 volt power connector:

This connector supplies power to the CPU and provides all power to the processor. One of the novelties that the EPS12V connectors incorporate is that the pins will not be divided into a 4+4 system.

8-pin (6+2) PCI Express power connector:

Even though a PCIe slot can draw up to 75W of power from the motherboard (24-pin connection), some components like graphics cards require more. When the component needs a high power supply, say 300 W, it will require this type of PCIe connection. In some cases, multiple connectors will be required.

SATA connector: 6 to SATA

SATA connectors generally supply power to HDD and SSD hard drives. In this case, in addition to the SATA power connector, you will need another data cable.

Modular and semi-modular PSUs

Most of the power supplies that we find on the market claim to be modular and most of them come with permanently connected cables.

This doesn’t seem like a problem. However, we are not going to use all the cables that it has and many of them end up stored in the box. Modular power supplies help keep cables tidy inside your computer.

Rails on the power supply

The rails are the cables through which the power supply distributes the energy. If we take into account the new ATX12V standard, they must be distributed as follows:

  • 3.3V: intended for RAM memory, but its use is becoming obsolete since most boards have VRM to power the memory that is fed from the 12V rail, which also supplies power to the M.2 SSD
  • 5V: These are responsible for supplying power to SATA devices such as the hard drive.
  • -12V:   obsolete
  • 12 V: Supplies power to the CPU, GPU, and fans

Will we have a new ATX12VO standard?

As we have seen in the previous point, the 12V rail is the one that feeds practically the entire system and the rest are becoming obsolete. The new generation intends to leave a single 12 V rail that supplies energy to the entire system.

This connection will require only 12 pins to connect to the motherboard, versus the 24 you need now. But for the moment we will have to wait for it to be adopted massively.

Power Supply Efficiency

The hardware of your computer is not prepared to use alternating current directly, so the main function of your PSU is to transform alternating current into direct current.

PSU efficiency is the amount of power wasted converting AC to DC.

An efficiency of 50% means that if it consumes 1000 watts, it is capable of supplying 500 watts.

These 500 watts are lost as heat and, in addition to showing up on the electricity bill, it also puts an overload on the fan. The 80-PLUS rating offers different energy certifications for efficiencies greater than 80%

80-Plus Efficiency Rating
80-Plus Efficiency Rating

Looking at the table above, Gold rated PSUs offer 87% efficiency at 100% load, Platinum reaches 89%, and Titanium is only 1% efficient (3% more than Gold).

In this case, we could say that it is not necessary to invest a large amount of money in a Titanium, since the difference in efficiency is not that high.

PSU Security

The power supply is a key part of our computer since any error can damage the hardware and all its components. The safety of the power supply can be divided into two: the one implemented by the manufacturer and the one that we have to take into account ourselves.

Next, we are going to review the most important security features:

  • OCP (Over Current Protection) – Prevents the power supply from receiving more power than it needs. It is designed to cut the power supply when the power it is receiving exceeds 130% of the specified.
  • OVP/UVP (Over/Under Voltage Protection): This security system turns off the device when the voltage exceeds 110% of the estimated.
  • OPP (Overload Protection): Protects against possible damage from overload.
  • SCP (Short Circuit Protection): Disconnects the power supply if it detects that a short circuit is occurring. However, for a short to be detected, a certain impedance threshold has to be exceeded, so not all shorts are detected.
  • OTP (Over Temperature Protection  ): The power supply shuts down if they detect very high temperatures. This overheating can be caused by a failure in the cooling systems.
  • BOP (Fall Protection): Prevents damage that may occur in the event of blackouts or power outages.

Silent or fanless power supply

If we remove the fan from the power supply, it will be silent. But a silent PSU and a fanless power supply are not the same things.

The main difference is that if we remove the fan, it will be silent due to the absence of a part. However, quiet PSUs minimize fan noise.

Most of the companies that sell silent PSUs use silent fans, even working at very high frequencies. For example, Corsair’s RM series offers a fan that only works at high loads.

In contrast, we find power supplies without a fan. They are not capable of supplying much power, since the components will overheat if they do not have a fan to dissipate the hot air. Seasonic offers some fanless PSU models, but the highest power is 500W.

Now that you know how to choose a power supply for your PC, which one are you planning to buy?

Also, read about How To Build Your Own Computer? Quick Guide

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Abram left his e-business studies to devote himself to his entrepreneurial projects. In 2017, he created the company Inbound Media and wrote articles about high-tech products for his Chromebookeur site. In 2019, Chromebookeur was renamed Macbound and became a general purchasing advice site. Today, Abram manages the development and growth of Macbound, surrounded by a young and talented team.

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