Graphic cards aren't getting any less powerful (or power hungry), so if you're upgrading from an older GPU to a newer model, you might be worried you'll also need to upgrade your PSU, too.
It Might Be Time for a New PSU Regardless
Before we dive into the ins and outs of determining whether the power load of a new GPU will necessitate a new Power Supply Unit to keep up, let's throw out a little PSU PSA.
PSUs don't last forever, and the build quality and efficiency have gone up over time.
Even if you're opting to reuse old hardware and just swap out your old GPU with a new one, give some serious consideration to swapping the PSU along with it independently of whether or not increased power needs call for it.
PSUs are critical PC infrastructure, after all, and it would be a shame to finally get your hands on a new GPU after dealing with a supply glut and scalper prices just to have it go up in smoke.
Determining If You Need More Power
The crucial question isn't just "does the GPU I'm installing consume more power?" The crucial question is, "Does my entire build, with the addition of the new GPU, exceed the recommended level for my current PSU?"
Because if you have a PSU with a significant amount of headroom, then there is no reason to replace it (other than replacing a really old PSU to play it safe).
Calculate Your Current Power Load
The key to answering our question is how much wattage all the hardware your PSU supplies require. We emphasize the word all because to answer your question accurately, you need to account for every single piece of hardware drawing from the PSU, including everything from extra drives to case fans---not just the flashy stuff like the CPU and GPU.
You can take the long-division approach to the problem, if you'd like, and look up the estimated wattage for every piece of hardware on your own and throw it all in a spreadsheet.
But why work that hard when we live in the future, and there are a plethora of handy tools to do the heavy lifting for you?
If you want a simple and reasonable estimate of the power demands your build imposes, you can head over to PCPartsPicker.com and "build" your PC by searching for the parts in your current build. Compare the estimated load to the rating of your current PSU.
If you want to check out both a basic and detailed look at your PSU needs, you can also check out the OuterVision Power Supply Calculator. Not only can you do the same plug-in-the-parts approach there, you can also really dig in with the Expert mode and tweak the results based on additional parameters like overclocking settings you've applied to your CPU and GPU.
For the sake of example, we ran calculations on a build with an AMD 5800X CPU, a GTX 1080 GPU, 32GB of RAM, some SSDs, and the secondary hardware like fans and such, and a 750W PSU through the calculators and arrived at an estimated load value of 445W.
Recalculate with Your New GPU
Once you've figured out what the current load on your PC is, you can replace the old GPU with the new GPU in your calculations. You won't always end up increasing the load, by the way.
Your new card might actually be about the same in terms of power demands or even a little lower than your old card. Either way, you'll have a new value to compare.
If you're going big, however, like swapping out an old GTX 1080 with an RTX 3090 Ti, for instance, don't be surprised to see a jump in the projected load.
When we swapped the GPUs in our calculation to a beefier model, our load calculation jumped to 675W. A 66% increase in power load isn't surprising given that the RTX 3090 Ti is a power-hungry card that pulls down around 450W compared to the 180W the GTX 1080 averages---a 150% increase.
If you're thinking that 675W is starting to sound like space heater territory, you're not wrong.
Compare the Current and Future Headroom
If you've been following along so far and running calculations on your hardware as we have, you have two numbers: the estimated power load for your old build and your new-ish build with the upgraded GPU.
Now it's time to talk about headroom and risk tolerance. Headroom is how much extra available power is left in a particular PSU's power rating after you've put it under load. There are some pretty strong opinions in the PC building community about headroom, including arguments that you should always have around 50% headroom.
Perhaps back in the day, running a lower quality and inefficient PSU with 50% headroom was wise because you couldn't trust it to truly perform as expected. But with modern, high-quality PSUs with proper efficiency certification, that's a bit extreme. Even with some PSUs getting a slight 2-3% efficiency boost when run at around 50% load, significantly upsizing your PSU just to get 2% efficiency return might be a bit much for your budget and needs.
In our original calculation, we have a 750W PSU with a 445W load. That load is approximately 59%, leaving us with a 41% headroom. That's a pretty substantial amount of wiggle room. You could even argue that if the build was destined to stay is it is without any upgrades, that might even be excessive.
Swapping out the older PSU for the RTX 3090 Ti, however, boosts our estimated load to 675W---dropping our overhead wiggle room from 41% to 10%.
That's not ideal, and we might run into issues, especially with the computer under a heavy load, with instability and even crashes. You might not, of course, and you could even slightly undervolt your card to fix that issue.
But this is why manufacturers say an 850W PSU is the minimum for the RTX 3090 Ti but recommend a 1000W PSU---if we rerun the calculation with a 1000W PSU then we boost that headroom percentage from 10% to ~33%.
The important thing is that you actually run the numbers for your particular setup and the demands of your particular GPU upgrade path, though, so you can get the right PSU for your needs and budget.