It can handle it perfectly well. Manufacturers exaggerate a bit on the power requirements of GPU's. Any half decent 400w PSU would handle a 9800GT no problem and since yours is a Corsair then no need to worry
You do not need to upgrade your PSU to use that card unless it doesn't have the right connectors (and you can't find adapters). When I say that I mean you need two 6 pin and you only have one or something. IIRC you should have no issues.