This is POSITIVELY THE LAST THING I WILL SAY ON THIS:
1. In over sixteen years of experience with IBM midrange systems, I have
never, once, seen an internal power supply unit fail.
On the other hand,
A. I have seen line power fail multiple times
B. I have seen UPSs from two different manufacturers fail with
absolutely no advance warning whatsoever
C. I have seen UPSs send "On Battery Power - battery nearly dead"
messages through the monitoring cables, during self-tests, on more than
one occasion, when there wasn't a damned thing wrong with the line power.
2. If, as you say, multiple redundant power supplies were not intended
to be plugged into separate power sources to guard against one of the
sources going down, THERE WOULD BE NO REASON FOR TWO SEPARATE AC CORDS.
The question is about monitoring for one or the other power source
cutting out at a time when nobody is here to notice, NOT monitoring the
UPS itself (which we do NOT do, PRECISELY because item 1C has occurred
on multiple occasions).
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