Yes, it will be no problem.
Dell underrate their PSUs - the actual peak output is actually considerably more (up to a limit).
I've heard people running the older, power-hungry 8800GT card that required additional external power from the PSU, on those 305W PSUs. They did it with SATA-molex & molex-PCIE adapters.
The HD4670 doesn't require this additional power, so should be fine. G