The GeForce GT 240 GPU card will draw a maximum of 5.75 Amps from the +12 Volt rail of the Power Supply Unit.
It doesn't have or need a PCI-Express Supplementary power connector since it gets all of its power through the PCI-Express X16 slot (i.e. within the 75 Watt PCI-Express Slot power spec.).
The Antec EA-380D Green Power Supply Unit, that rolli59 linked to, will do the job just fine.