The normal size case takes a normal PSU.
http://en.community.dell.com/support-forums/desktop/f/3514/t/19609538
I'm looking to upgrade the power supply of a Dell Optiplex 3020 Small Form Factor from it's default 255W to 400W in order support a new video card I will be installing.
I'm unfamiliar with the Small Form Factor models. Do they all use a default slimline power supply size? Or do I have to find a power supply that specifies my particular model - in which case, I'm only able to find replacement 255W units.

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