Eli5 techy: online calculator recommends 400W of power supply, but VGA recommends 650W, is there a problem going below recommended?


I’m about to upgrade my desktop computer. Using an online calculator and adding my components, it recommends a bit more than 200W of power. When I replace the VGA with the one that I want, it recommends 400W power. But when checking the VGA alone, it’s store page says: power supply 650W or more recommended.

My question is, I already have a 450W power supply, can I go with it? And what happens if the power is not enough? Will I risk any component?

Obs: Perhaps the calculator specifies raw energy, while the power supplies can deliver like 80% of what they say?

In: 1

Many power supplies can’t live up to their ratings

This was a big problem where power supplies would say 650W but 200W were available on the 5V rail and only 450W on the 12V but 99% of the power a computer draws these days is from the 12V rail. A good 450W power supply will be able to supply 37A on the 12V rail but a common one won’t

Go to /r/BuildAPC to check your exact specs but in general you don’t want to plan on running your components at 100% of their ratings. It ages them faster and a power supply’s capabilities drop as it ages and it’s capacitors don’t hold as much

400W? What calculator are you using? That seems _insanely_ low by today’s standards.

Regardless, the PSU is the one single component you never, ever want to cut corners on. Always get the absolute best one you can, and that isn’t always the one with the most wattage. Though you do want to overestimate the power draw, just in case.

Remember that your desktop CPU alone is going to use either 95W or 125W by itself, and an add-on GPU is going to add somewhere in the ballpark of 200-300, depending on the model. That’s 325-425 without factoring in any drives or USB charging capacity- solid state drives use less power than hard drives, but 400W is still uncomfortably tight for something you’re upgrading for gaming. I had an FX-8350 with an R9 280 a few years back that took a 700W power supply to run comfortably with a mechanical hard drive.

In a worse case scenario, it will explode because it had a bad fuse. In the best case, the PC will shut off because it doesn’t have enough power. The recommendation is what the computer needs to function, not what it will require while you’re using it. Intense tasks and long-term use will make it heat up, which makes it draw more power, both to cool itself and because it’s using more resources, and because heat changes conductivity.

Always go well above the recommended but stay within your budget, no need to say, jump to 800w.

Good PSUs will report a continuous power rating and a peak power rating. Continuous meaning if you run your computer 24/7 and it regularly uses 435W, you PROBABLY will be perfectly fine with a PSU rated for 450W continuous power output. That being said, some of your pc components, especially a modern GPU might suddenly ask for much more power from the PSU. In this case, you want your PSU to be capable of supplying a peak power output well above the potential power spike your GPU requests. 650W is a good amount for most desktops with a modern GPU. If you have a higher end GPU such as a 3060 or higher, you should consider a 750W or higher wattage PSU just to be safe. Another upside of high wattage PSUs is they’re often more efficient.

TLDR: add at least 20% to the wattage you need, to be safe. Find a PSU that says it can supply that wattage continuously, not just the peak output. Always buy name brand.