Guide to changing the power supply (PSU) of a desktop PC; what they are and how to connect all cables, connectors, sockets and plugs

PC power supply When your computer struggles to turn on or takes too long to start up, and when it makes too much noise, the problem may involve the PC’s power supply (also called PSU o Power Supply Unit): perhaps it is old and inefficient or underpowered compared to the computer hardware.

Change power supply it can become a way to save energy consumed by a fixed desktop PC, because newer PSUs are optimized to consume less energy. Replace the PC power supplyHowever, it may seem like something very complicated if you look at how many cables and connectors it is connectedbut there’s no need to be afraid, because it’s all about pulling out plugs and plugging them back in, without the possibility of making a mistake.

In the following guide we will show you How to change PC power supplyshowing you what you need to know and how to operate safely to change the PSU without damaging the PC components.

READ ALSO: What are the symptoms if your PC’s power supply is faulty or about to break?

1) Main components of a power supply

A PC power supply is composed not only of the transformer and the main switch with the plug, but also of a built-in fan and a series of cables and plugs that come out. Before continuing, it is worth understanding what are the cables and connectors that we find coming out of a power supply:

1) P1 (PC Main / ATX connector): it is the main cable with the largest socket that powers the motherboard and can have 24 pins or 20 pins with a small 4 pin plug that can be added. This connects to the socket on the motherboard which can be 20 or 24 PIN. If the motherboard has a 20 pin socket and the power supply has a 24 pin, you can connect it leaving 4 pins out on one side or you can use the ATX adapter.

2) P4 (EPS connector): this is the cable that powers the processor and must be connected on the motherboard, to a socket near the CPU. The extra 4 pins are used on motherboards that support overclocking to give more power. Most power supplies have two power supply cables, one 4-pin and one 8-pin, so you can choose the right one. If there is only the 8 Pin cable and the plug has 4 on the motherboard, you can still connect it leaving 4 pins out.

3) PCI-E connector (6 pin or 6+2 pin): The motherboard can provide a maximum of 75W through the PCI-E interface slot. This connector plugs directly into the graphics card in your PC. More expensive graphics cards require the 6+2 pin PCI-E connector.

4) Molex (4-pin peripheral connector): Molex connectors have been around for a long time, they are the plastic ones with 4 holes and two wires inside each one, one red and one yellow. In the past these cables were used to connect hard drives and CD-ROM players, but today they are no longer used (although power supplies still include them). Since they have been replaced by SATA cables, you will find the MoleX to SATA adapters included.

5) SATA connector: the SATA connector, with a flat shape, is the one that is connected to the CD Rom and the hard disk. A power supply should have 4 or more SATA connections, to support multiple hard drives. Thanks to their L shape, the SATA power connector can only be connected the right way.

The cables can already be connected to the power supply or can be connected later: in the latter case we are talking about semi-modular power supplies (where the only fixed ones are usually P1 and P4) e totally modular power supplies (with any cable that can be removed and replaced).

2) How to change power supply

To change power supply you must first unscrew the external screws of the case in the rear part (basically around the space where the switch and socket are) and then disconnect all the connectors that connect it to the motherboard.

In a modern PC we should first remove the main socket, the largest one, which requires pressing a lever in the center and then pulling hard to take it out, but without jerking, otherwise you can damage the motherboard; Below we can detach the disk connections, the connector near the CPU, that of the video card (if present) and any additional power cable.

Once all the cables have been disconnected, you can take out the old power supply. Once we have purchased a new power supply, we identify the various cables and sockets on the motherboard, place it in its housing, screw it in and make the connections, repeating the reverse operation for disassembly.

The golden rule when connecting power supply cables is never to force too much, use delicacy, do not use jerks and check the correct verses. If you use a non-modular power supply, it is important to put unused cables aside so that they can be hidden, collected and folded, including using cable ties.

3) Which power supply to choose?

As seen in the how to guide buy a power supply it is better to go to Amazon to choose a new one, since the prices are very good.

Among the different PSU models on sale we have chosen those that can adapt well to any standard home (i.e Mid Towerfor ATX or microATX motherboards):

  • Aerocool LUX550: 550 W PC power supply, 12 V socket, 88% efficiency with 80 Plus Bronze certification, non-modular.
  • NOX PC power supply URANO VX 650W: 650W PSU with 80 PLUS Bronze certification, 140 mm fan, dedicated PMW control system, extra long flat cable, non-modular.
  • ASUS ROG Strix 750W Gold: totally modular PC power supply with 80Plus Gold certification, ATX12V socket, ROG Heatsink heat sinks, Axial-Tech fan, 0dB technology, customizable and ON/OFF button.
  • Corsair RM750e (2023): among the best PSU models, thanks to the maximum power of 750 W, 80Plus Gold certification, 105°C capacitors, cables compatible with ATX 3.0 and PCIe 5.0, low noise system and completely modular cables.
  • SilverStone SST-ST85F-PT: one of the best power supplies on the market with 850W of power, 80Plus Platinum certification, 120mm fan and completely modular system.

To learn more we can read our guide on what a motherboard is made of and what size to choose.


If we did everything correctly just close and turn your PC back on, which should launch without problems after the update. In case of problems it is appropriate check the cables carefullyalso checking for have enough power for all components (especially if we use a dedicated video card).

To learn more we can read the guides above how to change your PC’s RAM, power supply and hard disk come on how to assemble the PC and fit the computer parts one by one.


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