Brother having APC Smart UPS 1000VA and I noticing high pitched buzzing noise coming from UPS: I think it from power filter capacitor - tall one you see on LHS of picture: 
(Picture all sourcing from http://www.elektroda.pl/rtvforum/topic843513.html, as brother not allow me open UPS)
I say this because UPS model 2003 and I know when electrolytic caps age, sometime their electrolyte dry, and hence making pitched buzzing noise?
Am I correct, or there be possibility transformer itself making high pitched buzzing noise (unlikely as noise intermittent and goes away for few seconds now and then)
That cap is 2700uF, 40V and I having hard time finding this cap locally. But I have 2200uF, 35V caps - so I thinking:
Connect two 2200uF, 35V caps in series to get theoretical 1100uF, 70V caps: calculation correct?
Connect two theoretical 1100uF, 70V caps in parallel to get theoretical 2200uF, 70V cap: calculation correct?
I guessing that tall cap 2700uF, 40V is power supply filter likely, so replacing it with theoretical 2200uF, 70V cap for confirming suspicion not bad?
I also have ESR meter: what value bad cap vs good cap read to confirming suspicion?
What other component possible make such high pitched buzzing noise from UPS? (UPS out of warranty since last 5 years and now obsolete model also, so APC not interested with feeedback)
Answer
For 2 use a 3300 uF, 40+ V. That is a more standard capacitance value than 2700 uF. And you may find others that are more than 40 V are available and those at 40 V.
For 2 your calculation is correct. However this reduces the capacitance so I wouldn't go that way. I would go with 4 or 5 instead.
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