dell poweredge t310

I have a dell poweredge T310 from 2008. It has a 400watt psu with a -5v rail and only 2 sata cables, 1 PCIe connector and a 20+4pin atx connector. I would like to upgrade my psu to one that has 2 PCIe connectors(for gpu's) and more wattage(550 watt). The newer psu's dont have the -5v rail in...