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Question about power supply compatibility with graphics card

By geramul
Sep 19, 2010
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  1. I'm getting a GeForce 8400 gs, and a 380W power supply.

    The graphics card says "Minimum recommended power supply with +12 Volt current rating of 18 Amp Amps." I looked over the power supply specs, and none of the 12v outputs have an amp rating of 18. I read somewhere though that you have to combine the rails to add up to the amp rating? I assume that's for high end graphics cards, where you have to plug the psu directly into the card. I don't know what a rail is, I don't know how it would work for this graphics card, since it doesn't seem to require the psu to plug into it directly, Iz confoosed.

    I am basically clueless when it comes to power supplies, so can someone please educate me in this, and PLEASE be mindful of how you explain it because like I said, I'm almost clueless about this stuff. Taking a couple more minutes to throughly explain this to me so I understand it well, won't kill you.

    I don't want to sound rude when I say this, but it annoys me when people do this to me. I honestly don't care what graphics card or power supply you have, if it's better than mine and you think I should get it. I am well aware that there are graphics cards, and power supplies, that are WAY better than the ones I chose. I chose these pieces of hardware because of my budget.
  2. raybay

    raybay TS Evangelist Posts: 6,908   +10

    It may be the way the specs are written on your PS... but
    The graphics card does care what the output is... more than the motherboard or other component does...
    A cheap power supply from 2005 or before had a better chance of not supplying the minimum power.... Now you can see all these specs for a quality power supply when you look at the descriptive information on the power supply section of Newegg, Directron, ZipZoomFly, cdw.com, and many others... but only in the past year or two has it all been published.
  3. hellokitty[hk]

    hellokitty[hk] Hello, nice to meet you! Posts: 3,415   +145

    Thats right, you're supposed to add up all the 12v rails for total amperage.

    Assuming your budget is ≈ $30 USD + ≈ $40 USD for an 8400gs, there are better options, the 4350 is actually about the same price. Depending on your current powersupply (please post any relevant information), you could skip a new powersupply altogether and opt for a slightly better card.

    Aside from the point:
    Basically I got that you have no idea what you're talking about yet decide that an 8400gs and 380w powersupply is absolutely what you'd like, and that you don't want to consider other options. It's kind of like asking knowledgeable people to screw in lightbulb for you because you think thats what you need to do; you really need to ask them which lightbulb you should be screwing in, then following their advice.
    That was my rant; I have an essay to write so it's nice to warm up.
    I don't think a paragraph like that is necessary. If you provide a tangible budget range, most people will stick to it. At the same time, we do realize that budgets are sometimes mailable and will provide possible suggestions slightly out of range if we feel that they have a worthy price/performance ratio.

    EDIT: Antec Basiq BP350 350W ATX12V v2.01 Power Supply
  4. Rage_3K_Moiz

    Rage_3K_Moiz Sith Lord Posts: 5,403   +39

    What is your budget like? And what are your specific choices? (links would be great)

    The +12V rail current cannot be added straight away, since the total +12V power is distributed over the rails, and the current rating for each rail is the maximum rating. For example, a PSU with two 18A rails does not necessarily mean that the total +12V current is 36A, because the total power rating for the +12V rails combined may only be around 300W, which means that only one of the rails can draw 18A at any given moment, and the other will draw only enough current so as to not go over the total power limit i.e. (300/12) - 18A = 7A.

    The total current is 300/12 = 25A.

    The above is assuming no overload conditions etc.

    FYI, Power = Current x Voltage

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