EVGA NFORCE 680I SLI 122-CK-NF68-XX - Manual (Page 49)

Installing and Configuring the EVGA nForce 680i SLI Motherboard
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number of the GPUs you install. If you are going to SLI two graphics cards,
you are going to require more power. As a rule, for one GPU you need a
minimum of a 350 W power supply. If you have two GPUs in an SLI
configuration, you will need a minimum of a 500 W power supply. To
calculate the power you are going to require for your specific configuration,
go to
www.slizone.com .
These instructions tell you how to install each of the parts listed so you can
have a functioning motherboard. As you go through the installation
instructions, we are assuming you have purchased the necessary parts.