Unless you are running a high end graphics card that is plenty of power.
Extra hard drives may add about 20w at startup, abut maybe only 10 once running.
A high end graphics card might need 50-200w, thats where you need some serious power supply.
For example my Intel quad core, 2 hard disks draws only 90w from the wall when running all 4 cores at 100% (SETI). If has a 450w supply, no worries. You wont be able to cram enough stuff into a 2U case to overload a 450w supply.
Ian