[GTALUG] Power Supplies & Video Cards

I know this really isn't about Linux per se, but I thought I would ask this question here any how. I have a computer wit a 300W PSU. It currently has an onboard video chip, which I would like to replace with a video card. Now, the video card specs mention needing a 300W PSU. My question is: Would that 300W requirement be a minimum, or what the card would need to work full-on? Thanks, -David