> Workstations should be on a Smart-UPS because the PSU capacitor won't have the capacity for a brownout with a Xeon-class CPU and multiple GPUs.

Also make sure it's rated for the load. My UPS went "lol nope" when I lost power while I was gaming, because I had forgotten about it when I went from single mid-range GPU to SLI top-end GPU...

Lots of users have desktops, monitors, chargers, and even heaters plugged into our UPSes. To them it's just a chunky power strip. They're lucky if they can squeak out more than 5 minutes on battery.

Well if I had one minute that would have been plenty. But mine went right into "overload" after a second and shut itself off.

Hold-up time is one of these things (besides long full-load life) that separates cream from crop in power supplies. High-grade ATX power supplies don't just promise 25+ ms hold up time, but actually deliver.

Some better review outlets test for that, since you can't rely on PSUs actually managing the spec-required 17 ms (I think that's the number, something in that ballpark)

Which reviewers do that?

Two come to mind immediately: https://www.tomshardware.com/ does. German magazine c't at least did, haven't looked at their reviews recently.

http://www.jonnyguru.com/ Has always done some pretty in-depth electrical profiling of PSUs. I usually check them when I need to buy one.

Tweakpc, hardwareluxx, c't, computerbase and probably a few more all use pretty high end ATE (Chroma loads and such) for their PSU tests as well.

c't still does very in depth testing like that when they do a larger PSU lineup test, though not for smaller individual tests.

I had 3 hard drives (likely) fail because of brownouts regularly occurring at a residence when high-amperage devices kicked on (power tools, air con, hairdryers, etc). The line would drop into the 80-90v range (120vac) which wasn't enough to turn anything off, but you could notice the lights "flicker." After a voltage conditioning UPS was added, haven't had a hdd failure

For situations where a UPS is too expensive or impractical you can also buy pure voltage regulators that use some kind of autotransformer, like the APC Line-R. I worked for an institution for a while that had every laser printer on one, there had been some bad experiences with losing laser printers to overvoltage incidents but they generally draw too much current to go on a UPS. I've also seen them used for A/V equipment.

Not always.

I have these.

https://www.apc.com/shop/us/en/products/Power-Saving-Back-UP...

They are line-interactive. Most of their "tower" UPS models seem to be Line Interactive.

Its those little ones that look like oversized surge protectors that usually are offline.

I have the next step up from this, the 1500 VA. I assumed the UPS under my desk was the Smart-UPS series but I can see it is the Back-UPS Pro. I haven't been in the office in months!

Looking at the schematics of some old models of BackUPS I found online the output relay needs to be powered in order to supply output from mains. Combine this with slightly funky internal power topology where +12V for internal logic comes mostly directly from the battery and it is pretty clear why battery with shorted cell(s) causes the thing to completely shutdown (probably even due to thermal shutdown of the LM317 in charging circuitry).

It's more complicated than that. There are Smart-UPS online. Thats double conversion also 0ms transfer

Some of the "newer" online models will have a green mode, which although double conversion green mode introduces a transfer time (~2ms, basically relay lift time).

Backups are also square wave, or stepped sine Smart are Sinewave output.

This is specifically APC.

Also remember there are tare losses (copper / magnetizing and conversions), so a UPS just sitting there can use up to 30W.

Corroborated!

Back-UPS stepped sine wave has about 3 square steps above or below zero, so it's a very rough approximation of a sine wave. Adequate for many kinds of equipment, but ugly on a scope.

There is, or used to be, a pin on the Smart-UPS line that you could tie high (or low?), to tell the device to operate in "Online" mode (inverter always active, line power continuously tending the battery). APC also sold it preconfigured that way as a separate, more expensive, product. :)

There's also a trick to jump-starting an unplugged-but-charged Smart-UPS. I've used this for several hours of remote power in inconvenient locations.

Quality devices, but test them regularly. The switch from idle to high-draw can be violent, and it takes out weak components. Similar to tungsten lightbulb filaments.

Oh, I know very well it's complicated. But that is the 500ft explanation I give to the beancounters, "why are we using these expensive UPSes when we can get them for $100 from Office Depot."

I'm most familiar with the APC line because that is what I use.

> the PSU capacitor won't have the capacity for a brownout with a Xeon-class CPU and multiple GPUs.

I'm not sure I buy that. The motherboard/GPU backplane VRMs alone should be able to buffer 20ms on these devices. Would love to see a test of this kind of thing.