Is a 650W power supply enough for overclocking

Buying advice for a PC power supply unit: This is how many watts you really need

Watts it can be

Manuel Schreiber

There are tons of PC power supplies on the market - in every price and performance class. However, not every power supply unit is suitable for every PC. We show you what to look for when buying a power supply and which models are recommended.

Do watts make their volts?

There are PC hobbyists who, following the motto "a lot helps a lot", simply plug a 1,000 watt power supply into their computer - whether the system needs the power or not. How many watts a PC power supply has to deliver, however, depends on the overall package.
For a typical office PC, 300 watts are usually sufficient, multimedia computers with gaming performance in the entry-level area consume around 400 to 450 watts and high-end PCs with a graphics card usually require a power supply between 550 and 650 watts. Only those who are thinking of overclocking and want to operate two graphics cards at the same time have to resort to even more powerful power supplies. These details are of course only guidelines, we will go into the topic in more detail below.
But not only the pure watt specification is decisive for a PC power supply unit. We'll show you what else to look out for when buying.

Energy efficiency: This is what the labels stand for

The power that the PC power supply unit draws from the socket never reaches the components 1: 1. How much or little energy is actually used depends on the efficiency - the higher this is, the more efficiently the power supply works. In other words, the worse the power supply works, the more electricity is simply wasted. It can happen, for example, that with a very poor 600-watt power supply, less energy is available for the components than with a high-quality 550-watt power supply.
In order to be able to see at a glance how efficiently a PC power supply works, many manufacturers have their devices certified. Depending on the performance, the tested models receive a corresponding "80 PLUS" label.
There are currently six degrees of efficiency:

Certification level and efficiency

Labelat 20% loadat 50% loadat 100% load

80 plus




80 plus bronze




80 plus silver




80 plus gold




80 Plus Platinum




80 Plus Titanium




With an 80 plus power supply unit, at least 80 percent reaches the components, with 80 plus titanium, on the other hand, at least 90 percent. The higher the classification, the more manufacturers usually ask for the corresponding model. From a cost-benefit perspective, the "80 Plus Silver" and "80 Plus Gold" variants are often worthwhile. The original 80-plus label, on the other hand, is hardly worth it anymore, and "bronze" is usually less recommendable as it is hardly cheaper than the "silver" and "gold" versions.
Conversely, "Titanium" in particular is often disproportionately expensive, so that the additional expenditure due to the low electricity cost savings would only pay off after many years - and then the lifespan of many PCs is exceeded anyway.

With or without cable management?

PC power supplies are basically available in two cable versions: one with integrated, i.e. permanently installed cables, and one with cable management. Cable management here means that all or at least some of the cables can be plugged in and unplugged as required, so that only those cables are installed that are actually needed. Another advantage of this modular structure is that the power supply unit can be exchanged very easily in the event of a defect - provided you buy the same power supply unit or at least from the same manufacturer. Because the connections to the power supply are not standardized, so that the cables are usually only compatible with the manufacturer's own product.
Nevertheless: For a self-made PC, we would rather use a modular power supply unit, as this not only makes the computer look tidier, but also makes it easier to assemble and replace. Even the air circulation can positively influence the reduction to the bare minimum. So the small surcharge is worth it.

Recommended 550 watt power supplies

In the following list we show you three recommended PC power supplies of the upper middle class with temperature control. The technical data of the products are comparable, but the Thermaltake power supply does not offer cable management - but is a bit cheaper than the competition. All of the power supplies presented are also available with more and less watts.

Price / performance (quality)

  • Very good
  • Satisfying
  • Bad

Specialist editors evaluate the products advertised by the dealers on the basis of qualitative criteria.

  • Corsair RM550x

    140 mm fan, with cable management, 80 plus gold certification

  • be quiet! Straight Power 11

    135 mm fan, with cable management, 80 plus gold certification

  • Thermaltake London

    140 mm fan, no cable management, 80 plus gold certification

What size does the power supply need?

The standard power supply for desktop PCs has the ATX format, which is attached to the case with four screws. For slim computers such as multimedia PCs, on the other hand, a more compact SFX power supply is often installed. The SFX power supply units save space in the housing, but the models usually do not offer as much power. The smaller fan could also turn up louder. To avoid this problem, there is the extension "SFX L", which is a little deeper and thus allows larger fans. Other, but less common, form factors include TFX, EPS and LFX. In addition, some proprietary power supply units are built into finished computers, which can make replacement considerably more difficult in the event of a defect.

Fan noise

Without a test, it is difficult to estimate how loud a fan is in operation. The fan size alone is not decisive here, but it is an indication. Many power supplies have a fan size of 120 millimeters, but some manufacturers also offer models with 130 millimeters and more - which, at least in theory, should ensure a slightly slower and therefore quieter operation. It is also important to ensure that the fan rotates in a temperature-controlled manner. Otherwise he would always give full throttle. Many well-known manufacturers also state the volume on their websites - the numbers do not necessarily have to be correct, but they can also be an approach.
Note: Do not try to change the fan on a power supply by yourself. Even when the device is switched off and disconnected from the power supply, there is a danger to life due to charged capacitors. If the fan is too loud for you, simply send the power supply back, and if the fan is defective, dispose of the entire power supply immediately.

Calculate power consumption

If you want to assemble your own PC, but are still unsure which power supply is the right one, you can have the power consumption calculated. The manufacturer "be quiet!" for example, offers a user-friendly online calculator that even takes into account whether the PC should be overclocked with the selected components. The list of results shows - understandably - only the manufacturer's products. However, you only need the calculated wattage here to be able to search, the rest can simply be ignored.
The PC power supply should ideally be around 80 percent full, as it works in the optimal efficiency range here.

Connection variety

Which connections a power supply unit should offer depends mainly on the intended use. Basically, however, if you want to assemble a modern standard PC, you don't have to worry too much about the connection options, because every current power supply unit has the necessary components.
These include: at least 4x S-ATA, at least 2x PCIe (8 pin / 6 + 2 pin) as well as an 8-pin and a 24-pin ATX connector. If you still want to connect old drives, you should also make sure that the power supply unit has Molex plugs - these are now rarely available with the power supply units, because all drives that are even remotely up-to-date use S-ATA.