If I have identified your card properly, the XFX 9800GT-512 requires a 400w psu with 26a on the 12v rails and a single 6 pin pci-e connector:http://www.xfxforce.com/en-us/products/graphiccards/9series/9800GT.aspx#4
If your card does not have a auxiliary 6-pin power connector, then the card will get the power from the pci-e slot only.
The simple answer is if a quality PSU has a 6 pin pci-e connector, it will deliver sufficient power to run the connector, along with a normal complement of other components. Such a PSU can be expected to be able to deliver the standard 75w to the pci-e slot also. Almost every psu has only one source of 12v power which it distributes among all the 12v leads.