I want to comment on the article's discussion of Cyberpower's "Adaptive Sine Wave". The article suggests the output wave form is a "modified triangle wave".
I did a search on Cyberpower's Site for "Adaptive Sine Wave" and got zeo hits. Nor did I get a hit on "triangular". The PDF user manual does mention "Adaptive Sine Wave" in the specs but does provide any further details as to the nature of the output wave form.
I bought a CP1500PFCLCD a few days ago and as part of my break in check I scoped the output while running on battery with a Fluke 97 scopemeter. The output appears to me to be a proper sine wave and looked better than the hashed up sine waves (with flattish tops and bottoms) delivered by my utility at the time. I did note some higher order harmonics but did not try to estimate the frequency or amplitude.
I mention this because it appears to me that the text in this now two year old article may be out of date or there may have been some confusion. And as mentioned in the comments here, the author(s) did not actually scope the outputs of these devices. I think they should have, and apparently could have acquired a visual only scope and least photographed the displayed output for illustrations.
I'll also point out that Cyberpower does make a slightly under $500 1500VA/900W pure sine wave UPS (model OR1500PFCRT2U) with specified runtimes that very closely approach the APC unit. Jus to say that Cyberpower's are not always as relatively underpowered. The runtimes listed here are simply based on the lower end consumer model that Cybnerpower apparently supplied. I do think it was a good model to add to the mix of reviewed devices. I just want to clarify the options available.
I'll add that my own run time tests were very consistent with the results indicated in the benchmarks. I did get confusing results on the first round of tests. I suspect that, as delivered, the unit may have been improperly indicating 100% charge while the battery was only partially charged. That might have corrected itself on its own if I had let the unit operate overnight before running any tests, and subsequent tests suggested reasonably accurate monitoring and results consistent with the benchmarks here.
I'm happy with the device so far. I bought it to keep a server, plus external drives, cable modem, router and switches alive during outages and allow for an immediate controlled shut down. With my expected 135W power draw I expect to get 40+ minutes of runtime, far more than I need. I saved anywhere from $75 to almost $300 relative to the APC options in the SMC/SMT lines. I could have gotten away with a lower powered unit, perhaps even the 850VA model, but the pricing of the 1500VA model was just too attractivbe to pass up.
Regarding the Active PFC issue, here is APC's published take on the matter:
http://www.apcmedia.com/salestools/RMUZ-7DTKRC_R1_EN.pdf
In reading it, it is not clear to me at all what the shape of the sine wave has to do with the problem of some Active PFC supplies shutting down when stepped wave UPS's kick in. They attribute it to in-rush approaching the rated capacity of the supply, even if the supply is lightly loaded.
But if that is the case then it is not clear to me why a pure sine wave UPS would do anything different. Personally I find that the APC article creates more questions than it answers but it is one of the few comprehensive discussions I've found that was written by either an UPS maker or a PSU maker.
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