Vital Information Regarding PC Power Supplies

Views 25 Likes Comments Comment
Like if this guide is helpful

One thing i hear time and time again from customers who purchase motherboards, video cards or CPU/motherboard bundles from me is that their newly purchased items "don't work". 99.9% of the time, this is not true, the items work perfectly... the problem rests with power supply unit the customer is using. I tend to focus on high-end PC components in terms of selling and for use in my own PC, and consiquently avoid cheap power supplies like the plague, and with good reason.

The first thing to look at with regards to a power supply is the connections available. Modern PC's will require a 24-pin motherboard connection and either a 4-pin or 8-pin 12v CPU connection. Some motherboards which require an 8-pin CPU connection can get away with having a 4-pin connector fitted, but don't count on this as my experience tells me more often than not, the PC won't boot, or is unstable as hell if it does. If you aren't sure which you have, you can either check your motherboard manual, or play it safe and buy a PSU that has a 20+4 pin motherboard connection and both a 4-pin and 8-pin CPU connection. These are actually quite easy to find. The next couple of essential connectors revolve around how new your parts are. If you have a PCI-Express slot for a video card, and are going to be using to be using a powerful gaming video card, you're going to need at least one 6-pin PCI-Express connector. With graphics cards becoming more power hungry, ideally you will want at least 2, since some require two 6-pin PCI-Express connectors per video card. There are some very high-end graphics cards that actually require one 6-pin connector and a new 8-pin connector, so check your graphics card requirements to see which you need. Note that the 8-pin PCI-Express connector is different to the 8-pin CPU connector that is used on a motherboard. Fixing the 8-pin CPU connector to your video card will almost certainly result in your brand new, expensive card becoming a smoking wreck in no time at all. The final important connectors are SATA drive connectors. With SATA drives well established as the norm these days, you will want a PSU with some of these.

There are adapters available for most of these connectors should they not be on the PSU you are using, but if you are buying a new mid-high end PC and your PSU doesn't have these connectors, the chances are it is not going to be adequate for your system anyway. Why? The next section will cover this...

Now comes what is by far the most important consideration with PSU's, the power output itself. Power supplies essentially split how the power is provided into 3 different voltages, +3.3v, +5v and +12v. These are known as Rails and power various components fitted according to their power requirements. In modern PC's the +3.3v rail is rarely used while the +5v rail deals largely with fans (particularly those attached to motherboard connectors) and drives. The most important is the +12v rail. This powers all of the most vital components in the PC, such as the motherboard, the CPU, the RAM and the video card. Modern PSU's will use up to 90% of their available wattage on the +12v rail. So, once you've got a rough idea of the watts required, you can then simply buy any power supply that has an output of that many watts, right?... WRONG! For one thing, a power supply's stated wattage is it's maximum, so if you have totalled up the wattage you need and it comes to 500, don't think a 500 watt PSU is going to do the job well. It's going to be constantly at it's maximum output, which will stress it considerably and lower its lifespan by a significant amount. Ideally you will want a PSU that has between 25-50% more watts than you require, to give it a safe amount of headroom not only for now, but also should you be planning on further PC upgrades later on. So, now everything is covered? Not yet it isn't...

Watts on their own are meaningless without amps. A power supply will have a label on the side of it showing the maximum amps on each of it's rails (as mentioned above). Modern PSU's often have the +12v rail split into 2 or more individual rails to provide a steadier flow of power to the components. When it comes to amps you really want an absolute minimum of 35 amps on the +12v rail (or total when adding each +12v rail together) if you are using a mid-high end PC. This is by far the biggest mistake made when buying a PSU, people will see the watts of the unit and immediately think it's going to be sufficient. Without good, steady, amps the unit is going to be pretty much useless. If you are looking at the description of the power supply and there's no mention of the amps, or no picture showing the label which lists the amps, ask the seller. If the seller can't tell you for whatever reason, you might want to err on the side of caution.

You are going to get what you pay for, if you think you're getting a bargain by buying something like an EZCool (by far the worst culprit) 800 watt PSU for about £30, think again. A quality 800 watt PSU with sufficient amps is going to cost you upwards of £80. Cheap doesn't mean cheerful when it comes to power supplies, and this is why so many customers buying new PC parts then assume their new hardware isn't working, because they've skimped out on the PSU. There are some ways of cutting costs of buying PC hardware, if you really must do this, but the power supply is most definitely not one of those ways. At best you'll end up with a PC that starts but will freeze at random times, at worst you'll end up with a PC that won't start up, or worse destroy some of your components.

The bottom line, check the connectors, check the wattage you need, then check the amps on the unit you are interested in. If the unit fails in any one of these checks, move on....


Have something to share, create your own guide... Write a guide
Explore more guides