I sit here quite hours and looking for differences for my old Seasonic SS330-GB and look the pictures for a SS380 and a Corsair VX450W. But the only differenz i can find is the capacitor, that seem to be more bigger in the VX450.
So here is the idea, replace the org. capacitor ( org. 180µF ) to a bigger one 250-280 for example and get more output Power on all rails?
If you cannot read and explain the schematic diagram of the device you are modifying you are just guessing. Why would increasing the capacitance of the component in question change anything?