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  1. Member
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    Just bought a refurbished PC to do some light gaming on. I'm trying to determine whether or not to upgrade my PSU. First I figured I better understand what makes a good power supply first. I've done a bit of research already and would like to confirm some things. I want to supply the needed wattage to my video card and from what I can tell this is supplied on the 12V rail. My questions:

    1) If a 300W PSU has a 20A 12V rail, that is actually better than a 350W PSU with 18A on the 12V rail?

    2) ANY video card that does not take a 6 pin PCI-e connector will draw at most only 75 watts of power?

    3) Assuming #2 and a good brand name PSU, If I itemize all my wattage by hardware and am under 80 percent of any rail, then i should be ok, right.
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  2. Mod Neophyte Super Moderator redwudz's Avatar
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    Simple test. Run the present PC at 100% CPU shown from the Task Manager for at least a half hour.
    Then check the heat exiting from the power supply. If it's 'hair dryer hot', you probably need a PS upgrade.

    And if the same kind of heat is coming from the PC itself (CPU, etc.), you need more cooling.

    I would recommend a 500 - 750 Watt PS. 500 is likely more than enough. 750 would be overkill, IMO, for most PCs.
    But larger PS's have become more efficient and somewhat cheaper.
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  3. You can use http://www.ocbase.com/ - multimeter (DMM) can be used to verify voltage quality (under load) - beware- DMM will not say everything about your PSU but it can be helpful to detect voltage drop.
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  4. Beware of ultra cheap power supplies. They often can't put out half their rated power before frying. If a mid range PSU costs much less than 10 cents (US) per watt it's probably trash. Stick with the big names.
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  5. Member bendixG15's Avatar
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    Careful of that word.....REFURBISHED....... it can mean just about anything.
    I learned a long time ago that certain cheap refurbished items become very expensive when they fail and kill other components.
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  6. Member
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    Thanks for the general understanding tools and tips! Actually haven't bought a Video Card yet either. Kind of confused on how to make a choice with that too... If I know the card only takes at most 75Watts(if no PCI-e Connector), why do manufacturers require different Amperage?

    https://forum-en.msi.com/faq/article/power-requirements-for-graphics-cards

    Seems to me, as long as the 75 watts is covered (~6.25A on 12V rail) then why would you need excess(understanding that I do not want to use more than 80% of any rail)? Of course I am assuming the wattage for the CPU and some other things in my estimate.
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  7. Originally Posted by GLE3 View Post
    If I know the card only takes at most 75Watts(if no PCI-e Connector), why do manufacturers require different Amperage?
    Because they don't know which power supply you're going to use and how much power will be available on each rail. And they don't know exactly what else you'll have in your computer sucking up power. And they're probably aware that many ultra cheap PSUs can't output half the power they claim. And of course, all that is too complicated for most people to understand. So they over estimate the size of the PSU you will need to make sure you'll have enough.
    Last edited by jagabo; 11th Sep 2015 at 11:35.
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