PSU Too Weak: What Happens?

Here’s what happens if your PC’s PSU (Power Supply Unit) is too weak.

The PSU is the heart of your PC ’cause it’s what keeps it going.

So if you want to know what happens if your PSU is too weak, then you are in the right place.

Let’s jump right in!

PSU Too Weak: What Happens? (Everything to Know)

Is Your PSU too Weak?

A PC without a power supply unit (PSU) is just an expensive heap of fancy hardware and circuitry.

While other parts of your PC are the skeleton, the brains, and the brawn, the PSU is the heart because it brings the whole unit to life. 

In order to make sure that your PC is operating at its peak, you will need a good quality PSU.

You can run into a host of problems if your PSU is low quality or too weak, including damaging or destroying your PC’s other more expensive components. 

This might surprise you, but in the worst-case scenario, an overtaxed PSU can cause fire and put your life in danger. Surely, you want to avoid that! 

Read on to find out how to tell if your current PSU is too weak and how to pick the right PSU for your PC.  

How Does a PSU Work?

Double computer power supply in the server machine.

A PSU powers your PC by converting energy from the electricity grid (AC power) to direct current energy (DC power) to power the components inside of your PC. 

AC power runs in multiple directions and can vary in magnitude, while DC power travels in a single direction at a constant volume. DC power allows your PC to operate stably and consistently. 

PSUs are built into some home PCs and can also be purchased separately if you are looking to upgrade your current machine or build your own unit. 

PSUs are sold in a variety of wattage options. Your power supply needs will vary depending on the type of PC you have and how you use it. 

How Much Power Does My PC Need? 

The amount of wattage that your PC needs will depend entirely on your PC’s specs.

The two components that require the most power are the graphics processing unit (GPU) and the central processing unit (CPU). 

The type of GPU and CPU you have will play a huge factor in the type of PSU you will need for your PC. 

GPU (Graphics Processing Unit) 

As the image and video creator, the GPU is one of your PC’s most crucial components.

It is also your PC’s biggest power consumer. The quality of your GPU will generally determine how much wattage it will require. 

  • Entry-level GPU: less than 100 watts 
  • Mid-range GPU: around 200 watts 
  • High-end GPU: 300-350+ watts 

Several things can happen if your PSU is too weak for your GPU. The graphics or videos can become corrupted, temporarily freeze, or completely stop.

In some cases, an overloaded PSU can damage your GPU, which tends to be much more expensive to replace. 

CPU (Central Processing Unit) 

As the brain of your PC, the CPU is another indispensable part of your PC.

The CPU requires a constant flow of energy to process data and run programs. The CPU is probably your PC’s second-biggest consumer of energy. 

Similar to the GPU, the quality of your CPU will determine how much energy it will need. 

  • Mid-range CPU: around 60-70 watts
  • High-end CPU: around 100-150+ watts  

Miscellaneous Power Needs 

Other parts of your PC that require energy to run include:

  • Fan/Cooler 
  • Random-Access Memory (RAM)
  • Solid-State Storage Device (SSDS)
  • RGB Lighting  

While all together, these miscellaneous parts generally do not require as much energy as the GPU or CPU, you should keep their energy requirements in mind when choosing your PSU. 

Unless any of these or other miscellaneous parts of your PC are highly specialized, they should consume only about 100 watts on top of your GPU and CPU. 

PSU Calculator

High-end system unit for gaming computer.

You can generally get a ball-park estimate for the amount of wattage your PC will need by adding up the wattage demands of your key components.

However, you should use a PSU calculator if you want a more precise answer. 

You can input a variety of information regarding your PC into the calculator besides just your GPU and CPU specs to get a more accurate idea of the type of PSU that would be most suitable to support your unit. 

PSUs come in a variety of wattages that range anywhere from as low as 250 watts to over 800 watts. The wattage amount is usually a hint regarding the quality of the PSU. 

  • PSUs that are 250-300 watts are generally lower or mid-range. 
  • A good quality PSU starts at about 400-500 watts
  • Higher-end PSUs generally start at 500-550 watts and go up from there. 

What Happens if Your Power Supply Doesn’t Have Enough Watts? 

There are a variety of problems that can arise if your PSU is too weak or doesn’t have enough watts to support your PC’s energy needs. Here are some telltale signs that your PSU does not have enough watts to support your unit:

  • PC not booting up 
  • Applications crashing, running slowly, or not running at all 
  • Shutting down suddenly 
  • Crashing and causing loss or corruption of data 
  • Getting a blue screen, otherwise known as the blue screen of death
  • Emitting a lot of heat 
  • A lot of noise when PC is running 
  • Smell smoke or burning 

If your PC is doing any of the above, you likely need a bigger power supply.

However, a weak PSU is not the only reason behind these problems, so make sure you cross off other possibilities before you go out and buy a new PSU. 

What Happens When a PSU Fails? 

Shocked woman in front of computer, inside workplace.

While you can step back and avoid overtaxing a weak PSU by reducing certain activities, once your PSU fails, you have passed the point of no return.

You will need a new power supply. 

Worse, a PSU failure can also damage crucial components of your PC that cost hundreds if not thousands of dollars to replace. 

Additionally, anything that was not saved on your PC at the time of the failure, for example, that term paper you were just finishing up, could be forever lost.

Even worse, a failing PSU can create a fire hazard in your home or office. 

What Happens If Your Power Supply Is Too Strong?

Now that we’ve determined that a PSU can be too weak and fail, it is time to discuss if the opposite can also be true.

Is it possible for the PSU wattage to be too high? The short answer is no, there is no such thing as PSU that is too powerful. 

Having more watts than you need will not cause your PSU to fail or any of the other problems associated with a weak PSU. 

It is pretty common to see recommendations online suggesting that more power supply is better. 

You will also see recommendations to automatically get a PSU that is 800 watts or more to be on the safe side. 

Here’s the truth:

While there is really no harm in getting an overwattaged PSU besides possible minor efficiency issues, there are few circumstances in which you will require that much energy. 

Those who recommend erring on the side of having more watts than you will likely use, worry about being able to support energy consumption spikes that your PC is likely to experience every once in a while with certain activities.

While they are correct in that you should have some overhead wattage to accommodate a spike in power usage, you do not need a PSU that exceeds your requirements by several hundred extra watts, especially if you are on a tight budget. 

PSU Capacity Considerations 

One reason why people suggest getting more watts than you need is that you should never run your PSU at full capacity at all times.

A PSU is most efficient when it is not running a full wattage load constantly. 

Ideally, your PSU should be running at 50% of capacity for most activities. If you regularly get to 60-75% of the capacity, that is okay too.

However, anything above 75% or so is considered running at a high capacity. Doing this constantly is not good for your PSU or your PC. 

For starters, running at a high capacity all the time will create a lot of heat and will be very noisy.  It is also a surefire way to overstress your PSU and increase the risk of it failing. 

If you are planning to constantly use your PC at a high capacity, you should get a PSU with some extra wattage as overhead to avoid constantly overstressing your system.

Besides that, too much extra wattage will neither benefit nor harm your PC. If you are not constrained by a budget and would like the extra watts, nothing is standing in your way!

Does a Higher Watt PSU Use More Electricity?

A PSU uses only as much electricity as your PC requires to operate. So, for example, if you have an 800 watt PSU but your PC only needs a total of 250 watts for a particular activity, your PSU will only use about 250 watts of electricity rather than the full 800 watts it is built for. 

The PSU will not use the maximum watts unless the PC requires that much energy for a particular function. 

Having said that, the efficiency of your PSU will determine whether and how much additional wattage it draws on top of what the PC requires.

All PSU will burn some extra electricity as heat. Less efficient PSUs will waste even more electricity than their efficient counterparts. 

Efficiency Ratings 

Some PSUs come with an efficiency rating, which certifies how well the PSU converts electricity to energy and how much of the electricity is lost as heat. There are currently six standard efficiency ratings: 

  • 80 Plus 
  • 80 Plus Bronze
  • 80 Plus Silver
  • 80 Plus Gold
  • 80 Plus Platinum 
  • 80 Plus Titanium 

The 80 Plus rating indicates that the PSU will convert at least 80% of the electricity into power for the PC and lose only as much as 20% as heat.

As you go up on the scale towards Titanium, the models become more efficient, losing less than 20% of the electricity as heat. 

80 Plus rated PSUs cost more than those that have not been certified.

There is a debate regarding whether the extra cost is worth the fairly conservative energy savings.

However, if you are not on a tight budget, a more efficient PSU cannot hurt. 

When To Upgrade Your Power Supply? 

Joyful gamer guy with his thumbs up, playing video games on his computer.

You might be wondering when to upgrade your power supply.

Obviously, if your PSU fails or if you are seeing signs that your PSU is overloaded, it is time to upgrade your power supply. 

Another reason why you might want to proactively upgrade your PSU is if you anticipate that your PC usage needs are going to go up. 

For instance, if you normally only use your PC to check your email or browse the Internet, which are low-wattage activities, but you think that you might want to take up gaming as a hobby, which is a high-wattage activity, you will need to upgrade your power supply to support this. 

Upgrading your power supply can ensure that your PC is more stable, running more smoothly, and that all of your components are better protected against damage and will last longer. 

Miscellaneous Considerations For Upgrading Your PSU

As discussed, wattage is the number one factor that you must consider when upgrading your power supply.

However, if you haven’t committed to a particular PSU model yet, there are a couple of other factors you should consider besides the wattage. 

If you are not on a tight budget, consider sticking with a well-known brand.

Even better, match the PSU brand to the brand of your other hardware. This will ensure that you are getting a high-quality product and that all of your components are working effortlessly together. 

You also need to pick the right size, which will depend on the size of your PC case. PSUs come in three general size categories, though other specialty sizes also exist: 

  • ATX, which is big and the most common (fits 95% of PC cases)
  • SFX, which is small 
  • SFX-L, which is a little bigger than SFX and has a bigger fan

Finally, consider the PSU’s cooling system or fan. Higher-end PSUs come with a fan stop mode or an automatic fan shut off feature when your PC is not being stressed with high-wattage activities. 

This feature not only reduces electricity usage but also allows your PSU to operate in a quieter mode.


  • Theresa McDonough

    Tech entrepreneur and founder of Tech Medic, who has become a prominent advocate for the Right to Repair movement. She has testified before the US Federal Trade Commission and been featured on CBS Sunday Morning, helping influence change within the tech industry.

    View all posts