Like the CPU and the hard disk, the PC power supply is one of the required computer modules. If the power supply breaks, it needs replacement. In this case, the defective component provides initial clues to find a comparable model. If you want to disassemble your PC yourself, you should pay attention to further points. The Watt indication alone is not decisive. Techsner reveals which seal you should pay attention to and what other properties count.

First of all: a current PC power supply must be able to

Provide enough Power: power supplies are available in different power classes depending on the application. From 400 watts it usually starts.
Provide sufficient connections: the model of desire should have enough connections for all installed components

Score with Extras: removable and sheathed cables (cable management and Sleeve) as well as a (semi-)passive operation are among the Extras, but go into the money.

Be prepared for the future: the optimal power supply is prepared for component changes, so it offers free connections and power reserves (in Watts). This is usually the case with brand devices

Why does a PC need a power supply?

Alternating current comes from the socket, but the PC components work with direct current. This results in the main task of the power supply: it must convert alternating current into direct current. In addition, each component of the computer needs a certain voltage, some even require several voltages at the same time. The power supply ensures that each part receives the necessary voltage. For this purpose, it distributes the current to different cables with different voltages.

How much power should the power supply have?

This depends on the area of application! A simple office computer without a dedicated graphics card comes with a 300 Watt power supply. A game PC, on the other hand, should have at least a 550-Watt power supply, because a powerful Pixel accelerator and a nimble processor thirst for power. High-end systems with more than one graphics card may need a power supply with 750 watts or more to satisfy the energy craving. In addition to the total wattage, the current on the individual lines and the total power of all lines (Combined Power) determine the application possibilities of a power supply. The manufacturers give Details on their websites and by sticker on each individual power supply.


There are calculators on the Internet that recommend suitable power supplies based on individual configurations. The power supply calculator from Be quiet is popular! which exclusively suggests suitable devices from the manufacturer. Alternatively, the calculator from Enermax with finer setting options is recommended. The Watt indication helps in the assessment, which power supply (if necessary from another manufacturer) is needed for your PC. Brands with good reputations include Corsair, Enermax, be quiet! and Seasonic.

What happens if the power supply is too weak?

Then the Computer can crash – for example, while playing games or playing a video. Because the components absorb so much power that the power supply can no longer reliably supply them with the required voltage.

How do power supplies differ?

Size: not every power supply fits into every housing. The manufacturers specify the respective size as a form factor. The most widespread is the ATX standard. However, Housing and power supply manufacturers do not always adhere exactly to the standard. Therefore, when buying a new power supply, you should compare the housing dimensions exactly with those of the shaft in the housing of your computer.
Connections and cable length: there should be enough and sufficiently long cables for peripherals. The current Minimum is two PCI Express ports (6+2 or 8 Pin), Four s-ATA ports for hard drives, SSDs and optical drives, two Molex ports for older drives, expansion cards and adapters. A 24-Pin ATX connector and an 8-Pin connector to supply the motherboard, processor and memory are mandatory. As a user of a small or medium-sized housing, you usually do not have to worry about the cable lengths; only in so-called Big towers you should study the information of the manufacturers in advance, so that you do not experience a nasty surprise when installing. By the way: some power supply manufacturers offer models on which the supplied power cables can easily be connected to the power supply by plug connection, often referred to as cable management. This saves unnecessary cables, reduces the tangle of cables in the PC Housing and thus improves air circulation.
Operating noise: in modern power supplies there is usually a fan with a large diameter (120 millimeters or more), whose only task is to keep the components in the power supply cool. Until the beginning of the 2000s, the propellers were responsible for cooling the entire PC, sometimes went to work accordingly loudly. Temperature sensors, optimized fans & co. ensure that the noise level on the part of the power supplies remains low during operation – according to the well-known manufacturers, who usually specify the volume on their websites.


If a power supply manufacturer wants to adorn itself with one of the coveted 80-Plus seals, the corresponding device must have a certain efficiency in defined load scenarios, which the Plug Load Solutions specifies.

What else makes a good power supply?

Efficiency: this value indicates which part of the energy absorbed by the power supply goes directly to the components in the Computer. The lower the efficiency, the more power the power supply converts into heat. For example, if the efficiency is 60 percent, 40 percent of the energy absorbed from the socket is lost. This increases the power consumption and the Computer must be cooled more elaborately. Good power supplies achieve an efficiency of 80 percent and more. They can be identified by the 80-Plus sign, which defines the efficiency in three load scenarios (four for 80 PLUS Titanium).
Voltage stability: power supplies must reliably supply the Computer with power. If the voltages are unstable, the PC may crash. Therefore, the output voltages in all power supplies are constantly regulated. However, the technology used (switching power supply) causes network disturbances, so-called harmonics. Therefore, there are mains filters in all power supplies that reduce these disturbances. The manufacturers call this PFC (“Power Factor Correction”). The passive and Active variant is to be distinguished, whereby the latter has prevailed due to better effectiveness.
Safety: a high-quality power supply has various protective functions. They ensure that the power supply switches off as quickly as possible in case of overvoltage (OVP), overcurrent (OCP), overtemperature (OTP) and short circuit (SCP). These functions protect not only the power supply, but also the expensive components in the PC. All power supplies sold in the European Union must bear the CE mark. Important: despite these protective functions, you must never screw on a power supply. Even if the power plug is pulled, very high voltages can still be stored in the power supply.

PC power supplies in comparison

With the collected knowledge it is now easy to find a suitable power supply for your PC. The PC power supply comparison is a good place to find out about the performance, equipment and noise level of the components. In the table, devices from Corsair, Thermaltake and LC-Power are juxtaposed. The comparison winner is the Top model and the price-performance winner usually convinces with a decent range of functions at a reasonable price.


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