I rencently bought an ATI Radeon 6850 that is rated for 500W PSU. I know I should have at least a 500W PSU, however, I am trying to recycle some parts from an old computer and have a 420W power supply which would be only 80W from the recommended PSU.

Could I run the video card reliably my 420W power supply or is the 80W just to big of a difference.

This person said they're running the card on a 350W PSU

This post says the card draws 150W at load

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    I cannot stress enough the importance of providing clean, proper power to a computer's components. You can save money elsewhere in your system, but I would never, ever, cheap out on a power supply. Get a nice high-efficiency 650W one and be done with it. You do not want to over-stress the unit providing a precise voltage level to your computer components. – Breakthrough May 24 '12 at 1:53
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    Since you mentioned old computer: in addition to what @Breakthrough said, 420W-rated PSU is not guaranteed to provide these 420W. All PSUs significantly degrade over time (capacitors age even if not used), and cheap ones were unable to provide 420W to begin with. – haimg May 24 '12 at 2:15
  • @Breakthrough: A high-efficiency PSU costs more than today's street price for a 6850. – Ben Voigt May 24 '12 at 3:53
  • the usual problem with PSUs is that they never provide their rated power(unless they are high end). they will always provide around 10-20% lesser than rated. Hence its better to buy a new PSU than getting poor performance from card; and worst case, frying something up.. – tumchaaditya May 24 '12 at 9:40

If you went to all the effort of getting a brand-new Graphics card, why waste all the potential with a sub-par power supply?

I recently upgraded my Graphics card to one that required more power, but forgot to check the voltage of my PSU. I instantly started experiencing freeze-ups and BSODs whenever I tried to do anything significant (past web-browsing), which went away when i installed a higher-capacity PSU.

I wouldn't try it, it's not worth it if you can't utilise the card anyway. Go and get a new PSU

  • Got a 600watt 85% efficiency PSU, you made a good point. – Nick May 24 '12 at 12:24
  • Glad I could help mate – Robotnik May 24 '12 at 23:39

This really depends on things like the efficiency of the power supply and how much stuff you have in your computer.

If you are running a relatively bare bones system without a ton of bells and whistles then you would most likely be okay.

That being said you should be fine, the worst that is likely to happen is some system instability if you do demanding things that require more power than the PSU can supply.

BSOD and the like. So I would try it and if it works then huzzah!

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    1. Using a non-recommended PSU probably voids the warranty of the graphics card. 2. If the PSU gets damaged by this, it might also damage other components. – Dennis May 24 '12 at 3:19

There is no such thing as a minimum PSU requirement for a video card. The only spec that counts is a certain amount of current (number of amps) that will be drawn from the +12V rail. The required power supply depends on the total power used by the video card, CPU, chipset, drives, and other components. And even there, the total rating of the PSU is pretty worthless, you need to check the current provided on each power rail.

Whether you have a 130W Bloomfield processor vs a 65W Deneb or Sandy Bridge is likely going to determine whether you need to upgrade the PSU.

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