General Question

Ivan's avatar

What happens if you try to use a power supply with insufficient power output?

Asked by Ivan (13479points) May 23rd, 2010

Long Version:

I bought a desktop about 4 and a half years ago. Later, I installed a dedicated graphics card, but it required a 400W PSU, so I bought a cheap 500W PSU to replace the existing 300W one. Now the 500W one is dead, and I’m wondering what would happen if I reinstall the old 300W PSU without removing the video card. None of the computer’s components are really worth anything to me, and I probably won’t actually do this; I just want to know what would happen if I tried it.

Short Version:

What happens if you use a 300W PSU with a video card that requires 400W?

Observing members: 0 Composing members: 0

5 Answers

jerv's avatar

It would melt.
It will almost definitely smell bad
It might catch on fire, though that is unlikely.
There is a chance of frying your motherboard and other components when it goes.

Noting good can come of it.

Ivan's avatar


Okie Doke

IchtheosaurusRex's avatar

It would probably work if you’re not doing anything extreme, i.e., gaming, with the video card. The power rating on the PSU is always in relation to the peak demand. Even at that, you’ve got some headroom by virtue of the capacitors. You could thus run your computer like this for a while, but it would be a good idea to replace the PSU with one that meets your power demands soon.

As to what will happen, no it’s not going to melt down. They do have fuses, you know. If you exceed the PSU’s output capabilities, you’ll get a voltage drop on one of the lines, which would probably cause your computer to shut down. This could be a problem if it occurs during a disk write when you have write-behind caching turned on.

Ivan's avatar


I played it safe and removed the video card. It’s a pretty useless machine now, but at least it works.

ApolloX64's avatar

First, use this:
Enter your details and see what happens. Generally, you can use a lower wattage PSU as long as it is a quality one. You won’t damage anything immediately, and if your overall usage at 80–100% TDP is just over the PSU you’re putting in you will be fine.
Inadequate wattage causes heat buildup which will damage circuits over time. If you notice your system crashing, hanging, BSOD’ing or other odd behavior it has never done before then you’re in trouble.
Most PC’s, even high powered rigs don’t NEED a massive PSU it is just good to have the extra headroom if you run into issues or want to add in more hardware. A Quad Core with 4GB of DDR2/DDR3, a single SATA HD and a DVD-RW with a quality motherboard and power supply and maybe an HD 4800 will consume between 330–450W, while a system running the same with a GTX 260 will be around the 500W mark.
Antec, Thermaltake, Seasonic and Enermax make excellent quality PSUs that don’t cost a whole lot, so think of investing in one of those soon.

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