Remote sense without load
It will not hurt anything to connect the +RS to the +12V and the -RS to GND.  In fact, as shown below, there is probably already an high resistance internal connection so that the supply will be able to regulate without external sense connections.  Connecting the sense externally with wires overrides the internal sense resistors.

Assuming that the supply is not defective, since the supply is putting out +12.8V both unloaded and loaded, the output voltage may actually be set to +12.8V.  This page about Hacking HP Common Slot Power supplies - 12V@100A may be helpful in working with the DL580.  Unfortunately, I could not find any specific information about setting the output voltage.



(From Power supply “Remote Sense” mistakes &amp; remedies)