You more or less answered your own question, in that you purchase a UPS without electronics trying to allocate and measure load.
First, I didn't ask a question! I made a statement of fact. And second, you size a UPS with AVR based on the maximum load the UPS will encounter from all the connected devices and that gives you the minimum size UPS to get. You can always go much bigger for longer run times.
That 354 surge protection joules rating on a $150 unit is really going to protect anything?
Ummm no. Now I understand your confusion.
Sorry but you don't understand the function of a UPS with AVR! You don't compare the joules rating of a UPS with that of a surge and spike protector. Why? Because a UPS with AVR is an "intelligent" device and it is NOT designed to absorb
excessive voltages like a surge and spike protector does. You are right that a quality surge and spike protector would have a joule rating MUCH MUCH higher than 354 joules. A surge and spike protector should be rated into the several 1000s! Not necessary with a good UPS with AVR.
And it appears you don't understand the difference between a UPS and a UPS with AVR. For computers systems, you buy a UPS with AVR. NOT a criticism - just an observation about a common misconception about UPS with AVR vs surge and spike protectors.
You are buying a UPS for continued operation during power events, not for protection.
NO!!! You can keep saying that but it is still wrong!
For my garage door opener and outdoor security lights, as examples, you would be right. For them, a "basic" uninterruptible power supply (UPS) or "battery backup" is fine. But for computers, home theater audio equipment and other sensitive electronics, you buy a USP with AVR
for protection from power anomalies, as well as for its automatic voltage regulation - or "conditioning". As I noted above, backup power is just a minor bonus feature. It IS the AVR that matters most.
Modern PC power supplies are quite tolerant to their input voltage and so might not have a need for an AVR
Yes and no. They are quite tolerant from "normal" (i.e., minor) surges and spikes typically seen many times each day. But not big surges and spikes. Those may not take out the PSU, but constant banging ages electronics. And if excessive, it surely can damage the PSU. The ATX From Factor requires all ATX PSUs designed for 115VAC operation to maintain proper DC output with AC in from 90VAC to 135VAC. Above that could damage the PSU, below and the PSU "should", I say "should" shut down.
No surge and spike protector, include the Furman can adjust for such low voltage events. But an UPS can. Same if the input voltage increases above that 135VAC threshold - which could happen if the transformer feeding your home malfunctioned as recently happened to me.
Then again a UPS with AVR is rather important so the battery does not have to keep kicking in.
^^^^THIS^^^^ The AVR again is an intelligent features that regulates or conditions the voltage when it deviates, if it can. If the deviation crosses designated thresholds, it cutover to battery.
And again, we are not just talking about "protecting" the computer PSU. A properly sized UPS with AVR will also "protect" our monitors and all our network gear too.