What Is the PSU?

The PSU or Power Supply Unit is one of those components that seems to get left out when upgrading your PC. We all spend our money on a new CPU / Motherboard combo, More RAM, bigger Hard Drive or more powerful graphics card but when do we shell out any money on upgrading the PSU? Ultimately the PSU could be the most important upgrade you can make. If your adding components all the time into your PC, having more powerful graphics cards and processor your current PSU will come under more and more strain. A step too far and the power to your system will become intermittent and causes random re-starting of your computer or may fail to start altogether.

You may be surprised at the amount of choices you have when looking to buy a new power supply unit. Not just in manufacturers but also in capacities. What I mean there is the capacity of watts the PSU can output. This is the main selling feature of the PSU but should not be used as the one and only measure. The output capacity is measured in Watts. The quoted capacity you see when looking at PSU's is the total wattage that the PSU can output at anyone time, it is rare however that the PSU will ever be able to output that total. The reason for this is the way that a PSU is set up, using several connections of differing voltages and currents each having reserved a certain amount of power from the PSU. Unless all of these are used at once the PSU will not reach its full potential.

What does the PSU do? Power Suplly Unit

The PSU is the component inside your PC that is tasked with the job of taking the AC (Alternating Current) and convert it into DC (Direct Current) at varying voltages depending on the requirements of the components. Quality of PSU's can vary a great deal, ranging from total output wattage to efficiency. But all of them carry out the straight forward task of supply the right amount of power at the right voltage to the internal components of your PC.

Staying on the Rails

The Power Supply unit as we said produces a DC output at differing voltages. Each of these are supplied via different "rails". Each Rail has its own set of circuitry and specific voltage dedicated to a specific set of hardware. The types of Rails include a 3.3V 5V and 12V. They also include a -12V rail (this rail has nominal power capabilities) and some have a 5VSB rail especially for use when the PC is in standby mode. Modern Power Supplies have more than one 12V rail as more and more components inside the PC require this rail. These rails have to be separated in order to keep the current at an acceptable level. Under too much load on a single circuit the wires could easily melt and possible cause a fire.

Myth Busting

The first and probably most important myth to quash is that a larger power supply (in terms of total power output) required more electricity to run. This couldn't be further from the truth. Your PC will only use the amount of power that it requires and any given moment in time. If you have a PC that doesn't require much power then it wont draw any more power with a larger power supply. But if you upgrade your components or add components a larger power supply will be able to handle it a lot better. It is also thought that PSU's operating at a fraction of their capacity actually operate more efficiently therefore saving power and money when in operation.

The new modular PSU's are better because of the space saving design? The modular plug is a useful connector that allows you to only connect the power cable to peripherals that you are using. This has its advantages of having a cleaner looking case and better airflow around your PC aiding lower temperatures. There is however a downside to modular connections, that is the fact that adding this type of component adds to electrical resistance from the power supply. This in turn decreases the efficiency of the PSU and causing extra power to be wasted. Professional system builders seem to sway towards the power saving of the standard model than the more elegant modular system.

Two PSU fans are better than one? Usually two is better than one, but in the case of the PSU, there really is no advantage of having the extra fan. The tiny space in which the PSU operates in does not have enough air around it to require more than a single fan. Only 1 fan can be dedicated to exhausting the hot air in such a small space, so the second fan can only be used to cool a specific area. This would lead you to believe that the PSU has a manufacturing problem that requires this extra spot cooling or the second fan is just a selling gimmick. Don't choose a PSU based on the fact it has a second fan.