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How to handle frequent temporary voltage drops on input side of SMT1500C?

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How to handle frequent temporary voltage drops on input side of SMT1500C?

This question was originally posted by Bernhard on APC forums on 8/3/2020

Not sure where to post this, since it is only tangentially related to my UPS, so hopefully this is a good (enough) spot.

I am using an APC SMT1500C UPS (with an AP9631 NMC2) to protect my networking gear, my NAS and my desktop from power outages (utility power is 120V nominal). My house-mate uses an old window air conditioning unit in his room, which is unfortunately on the same circuit as my home office. Every time the a/c unit's compressor kicks in, my UPS registers a voltage drop below 106V and about a second later a return of the voltage to normal. I suppose the inrush current for the a/c unit's compressor is the root cause of the temporary voltage drop.

This is in the U.S., California in a residential home with 120V/60Hz nominal voltage/frequency.

Yesterday (a weekend with hot weather) I got these messages about 14 times, though usually it's quite a bit less. I understand that I could lower the "low voltage boundary" on my UPS, but I actually want to protect my gear from a temporary voltage drop. Without my UPS, my NAS and my desktop wouldn't survive the voltage drop without a reboot.

* It is correct to assume that every time I get this message, my UPS will switch to battery power and then back a second later? If so, am I correct in assuming that this will wear out the relays on my unit prematurely?

* Since I'm looking for a "pluggable" solution that doesn't involve opening the a/c unit and installing a capacitor to buffer the inrush current, I've read that there is a type of product, called a "soft starter" that might help solve this problem by limiting the inrush current to the a/c unit's compressor.

Does anybody know of such product for the U.S. (120V, NEMA 5-15 plugs and receptacles, suitable for air conditioners) at a reasonable price (say less than $100-$150)?

Or perhaps there is an altogether different solution for this? Or is this perhaps a non-issue, because the SMT1500C's relays can easily handle 10000-20000 toggles over their life-time, even under load.

I would appreciate any advice on how to best approach this problem. Thanks in advance for your help.