For a system with a single Radeon HD 5850 graphics card a minimum of a 500 Watt or greater power supply with a combined +12 Volt continuous current rating of 26 Amps or greater and with at least two 6-pin PCI Express supplementary power connectors is recommended.
Your Delta Electronics, Inc. Model: DPS-460CB A power supply unit has a maximum combined +12 Volt continuous current rating of 31.5 Amps. What it lacks is two 6-pin PCI Express supplementary power connectors. You could use Molex to 6-pin PCI-E adapters but the problem is that the connector distribution on the +12 Volt rails is unknown. If all four Molex connectors are on the same rail you will trigger the rail's current limit protection circuit (+12VA@10A, +12VB@11A) shutting down the power supply unit.
A reference clocked Radeon HD 5850 graphics card itself may draw up to 12.6 Amps from the +12 Volt rail if you were to run a GPU stress testing app like FurMark or OCCT or if you were to overclock the graphics card. This would exceed the current limit of either rail +12VA or rail +12VB.
I would suggest a new power supply unit that actually has at least two PCI Express supplementary power connectors.