Xps gen 4 desktop power supply upgrade possibility

Question

I just bought a Radeon HD 4870 X2 2GB video card. It requires a 750W power supply with at least one 2x3 and one 2x4 PCIe power connectors. My current power supply is 460W and has one 2x3 PCIe power connector. My power supply part number per dell rep is w7124.The part numbers I saw online are: Manufacturer Part# : XH732Dell Part# : XH732Dell does not have any compatible upgrade for my system. I have called around, and due to the ackward placement and shape, finding an upgrade is virtually impossible it seems. thank you for your help