When auctioneering isolated low voltage DC power supplies for redundancy (24 VDC) is it sufficient to use diodes in the supply (+) side only? From a circuit perspective it seems reasonable but is there a reliability concern?
It's done all the time. Make sure that the i[²]t rating of the diode is significantly larger than the i[²]t of the largest fuse you plan to install on the autioneered output. That way the fuse blows to isolate the channel and protect the diode instead of the diode blowing to save the fuse. You can end up with some big diodes but you won't need to fit them to huge heatsinks because you don't need their continuous rating.