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I have opened up my tower and looked at the power supply case and all the numbers on it. I am very lost.

I want to install a second graphics card into my machine so that I can connect a second monitor to it (the onboard graphics card only has 1 VGA/DVI port), but when I try to install it, my power supply can't handle it (computer won't boot up).

What do I need to consider when getting a new power supply, and where can I find out this information? I have downloaded a piece of software called CPU-Z and that provides me with a lot of information about my computer.

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To get the best answer, add in the make/model of the motherboard and graphics card or the make/model of the PC to your original post. Manufacturer's often include power requirement calculators on their websites so knowing make/model is very helpful. – Tog Nov 3 '11 at 7:45
As a side note, don't skimp on PSUs. Always stick to well-known brands (Antec, Corsair, and Seasonic, to name a few). It's not only the name you're paying for, but the quality and the support. – happy_soil Nov 3 '11 at 12:09
Motherboard: ASUSTeK Computer INC. Model: M3A78-CM Current Graphics: ATI Radeon 3100 Graphics Card I want to install alongside: ATI Radeon X1300 Thanks for suggesting me those calculators guys, but I've checked those out earlier and they have like 50 options for which I don't even know what to put. I'm not even sure what's the number I'm trying to get out of them. By what aspect do I rate power supplies anyway? And thanks, all your help is appreciated :)! – ExitFailure Nov 4 '11 at 2:35

You can try using some software, there are online tools that did what you want:

Thermaltake Power Supply Calculator

eXtreme Power Supply Calculator

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Basically, what do I need to consider when getting a new power supply

You need to know:

  • Your existing power supply specs - there should be a sticker on the PSU with numbers like ( 400W, 70%, 24A Dual Rail etc).
  • Current computer details ( processor type, number of hard drives/optical drives, presence of a graphics card)
  • Existing Power supply consumption - You can perform a rough estimate using power supply calculators such as the ones posted by Marcx
  • New graphics card power supply consumption - you can know about it this by reading reviews of the graphics card.

So, the new PSU should be off Existing Power Supply Consumption + New GPU consumption (assuming you don't have any existing GPU - if so - this should be the difference of the two) + 10% buffer/reserve capacity. Just in case.

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