To use redundant power supplies on IDUs other than the original Giga, simply connect two -48v power sources to the three pin power connector. The -48 source from each should be on the two outside pins and the ground is shared on the middle pin.
The IDU will share power off both supplies, or use whichever one has the higher voltage. i.e. If you have a supply running at -52 and one at -48, the IDU will take power from the -52v supply and use the -48 as backup. For this reason it is recommended if you have a battery system that you are planning on using as a backup, it should have a lower voltage than the primary supply.
The IDUs will accept a voltage as low as -36, but the closer to -48v the better.