Some interesting comments from people that have experienced the same thing on reddit:

One guy got a video of his burning up on his Ring doorbell as he rushed it outside:

Tear down:

I have contacted CyberPower for more information.

I have one of these. I have had it for years, and even swapped out the battery pack once. I have had no other issues with it.

After I read the Reddit post and watched the tear-down video, I disconnected and opened it up and found that not only did it have the yellow glue, but patches of it had turned brown and had what looked like drops on it in places.

Now I am looking for a replacement, but from the comments here it sounds like other manufacturers have the same issue.

I woke up one night to that horrible burning motherboard smell. Ran into the office and noticed it was the UPS. Somewhat freaked out (would have never expected that to go on me in this manner). I unplugged it ran downstairs and put it in the middle of the driveway. After watching it for about 10 minutes I went back to bed. Disposed of it two days later (after taking the battery out to eliminate a runaway effect.
I just got what I think is very poor response from CyberPower who tried to discredit the people posting the videos:

"Thank you for contacting CyberPower Technical Support.

We are aware of the video and we totally understand and appreciate that you brought it to our attention to confirm this.

The person who posted the video offered no evidences to support his claims in the video as he only used assumptions.

There were no presentation of test results or industry data provided to prove his claim. CyberPower products are UL listed for safety and the rubber glue we use is also UL listed. Finally, CyberPower has thoroughly tested the rubber glue we use, and our results are aligned with industry information meaning there is no danger of the UPS catching any unfortunate events or shorting out as a result of the glue. The results debunk the claims being made in the video.

I hope I have shed a light about this concern. Rest assured that all our products are safe.

Regards, Technical Support CyberPower Systems Inc."

Yes, mine did just that last year. Popped during a power outage, they gave me a new one, no questions asked... So they probably know about this?
This is a problem with almost all modern UPS's. I had some of the old APC's that had the aluminum case with the high quality circuit boards with adjustment pots. These units were purchased in the mid to late 90's and were rock solid, I finally retired the last one about two years ago because it ran out of adjustment on the pots.

I've have numerous later model UPS's made by APC that have gone up in smoke when they were needed most or just up and die for no good reason. The units I have now are supposed to let me know when the batteries need to be changed, but that feature is a total failure.

In summary, all modern UPS's are junk.

Glue that breaks down over time, into something that can conduct electricity.

A forum member on that post says that they've seen the same epoxy compound on various electronic items from 1970s, 80s, 90s.

Would be nice to know what other people recommend for UPSs with sine-wave output.

Small APC units are pretty crappy by my own experience as well, especially if you go below 700VA.

I've used several 1000VA back-ups, smart-ups, and while the build quality is generally ok, the trip time for triggering and voltage upregulation was next to useless (passing >500ms). Many back-ups units tend to trigger the differential. The batteries you get from APC itself are just plainly overpriced.

I generally prefer to have many smaller upses nowdays, so I went with a few back-ups rs 500 and two cyberpower (cp900epfclcd).

Upregulation of the rs500 is a joke that you cannot rely on. The output quality is "passable" at best. It's also a pretty basic plastic case, pretty much like the cyberpower. When powered off, it keeps on flipping the main input relay every 10 seconds until it's fully disconnected from the mains.

On the other hand I didn't own cyberpower units for 10+ years like I did for APC, so I cannot truly comment on that.

Can somebody recommend alternatives that truly perform their duty?

Thanks so much for posting this. I have one of these in my office. I just turned it off and unplugged it. It will be going to the dump tomorrow.
A different less catastrophic problem with at least the CP1500PFCLCD is that if it detects a battery or charger fault, instead of continuing to run in bypass mode, it is designed to immediately cut all power to the load until it is power cycled. As far as I know, this behaviour is not documented anywhere, so you only get to find out when it is too late.
The first place I ever saw a CyberPower was years ago on an Amazon sale. I was not familiar with that brand and much more aware of Tripplite and APC gear. I assumed it was some sort of cheap knock off available from Amazon only.

I have no idea about this company, but they were definiately part of the collateral damage of me being highly suspect of any thing on Amazon that is from a brand name I am not personally familiar. I don't know if that says more about me, Amazon, or CyberPower.

I had to place my unit (CP1300EPFCLCD) in an empty room for 2 weeks to let it out-gass, the smell of plastic was unbarable and was not suitable for living conditions. I found others complain on the web just as well.

After two weeks I measured the amount of VOC in the room for a couple of hours and there was still some presence but nothing to worry about.

Overall the unit works as intended ...

Yeah, I came across this when I was researching UPS models since I have a few I need to replace with sine wave units. Unfortunately the current generation of APC's consumer PFC UPSes also have a reputation for catching fire.

At least this is a cause I can pre-emptively fix ony own, I guess.

Solar "all-in-one" inverters are a good alternative to a UPS and fairly inexpensive. (~$400 for 1kw). Solar panels aren't required, just bring your own battery (lead acid or LiFePo)- you could even pull the batteries from your existing UPS.
have a couple of those... i guess now

step 1: exploratory surgery of UPS

step 2: finally install new smoke detectors

The real bummer it's that I got 20kw of batteries a few months ago but they don't kick in quick enough compared to ups, so need keep on using ups

I was just looking up UPS models, I have the CP1500AVR, is that effected? It looks like all the complaints are on the PFC. I was getting wary when I saw some Amazon reviews mentioning fires including the EC850LCD. I've also read fire stories from APC. The Amazon site has the APC Gaming UPS even having countless reviews about it popping, smoking, or catching fire. So, I don't know which company to trust.

I have also wondered how many reviews people are getting counterfiets. It's hard to tell anymore.

I just took apart my unit CP1300EPFCLCD and it indeed has the yellow silicone. There's also a lot of white silicone but only to keep wires in place.

My solution is to just inspect the unit every once a year to see if any yellow glue is turning brown just like in the video. Meh ...

Edit: A closer look showed that some parts of the glue already turned brown. It seems to be affected by heat because the parts that are brown are the parts making direct contact with the board/components.

Could this kind of issue be avoided, at home, by simply setting the connected device to shutdown on power interruption?

I have a UPS connected to a NAS and because it is non critical I shutdown after 1 minute of lost power, and I think it can turn back on automatically when power is restored. I only care about data integrity, not uptime.

Isn't it UL-certified though? I would think they'd check for hazardous glues as part of said certification.
For what it's worth, the CP1350PFCLCD I had died a strange, non-charging death where it would take about two weeks for the battery to discharge and start screaming (while being plugged in). Serves me right for cheating on APC.
I’ve had so many of these because it’s the model CostCo sells. They often fail randomly, but otherwise have been okay. I wonder if this is why they fail so often.

Guess it’s a good thing I switched to Tripplite.

My APC unit did that too.

Be sure to install extra smoke detector around your PC area.

I have one of these units. It's fortunately powered off, and have been for awhile now. Kind of concerned to turn it back on in the event I'd need it.
Does anyone here have a UPS for their Synology? If so, what did you choose? Do you like it?
so how do you go about removing/cleaning that glue?