It definitely can, it's more than enough. Depends on the video card. If you're spending $300 on a video card, your not spending $25 on a 400w PSU. If you're buying a $350 card, you need a minimum 500 watts. Which is why Jay said correctly it will power really any single gpu on the market. Now in crossfire, definitely not.400 W is very low. I don't think it can handle medium tier graphic cards.
Good deal for people who only use a computer to browse, email or watch youtube though.