There are at least three common types of power conditioning:
(a) Voltage Regulation - ensures the voltage delivered to the load is constant. This may include voltage surge (spike) protection, but does not include maintaining power when the main feed fails.
(b) Surge Protection - cuts off brief increases in Voltage (spikes) so the circuits in the load are not damaged, no other protection.
(c) Uninterruptable Power Supply (UPS) - maintains power to the load for some significant time period after the main supply fails, also acts like a Voltage Regulator and should include surge protection.
The damage you described COULD have been caused by sustained low voltage in the supply, but more likely by voltage spikes mixed in with all the other supply misbehaviour. So, assuming the SAME things can happen again, you might need only surge protection. BUT if you want real peace of mind you probably do want a GOOD UPS.
So what is that? Output waveform is one thing. A UPS keeps its battery charged from the normal power supply and, when that supply fails, it draws power from the battery, converts that to 120 VAC, and sends that to the load. HOW that conversion happens determines the waveform. One way is to use a real sine wave oscillator at 60 Hz and then run it through a huge amplifier, basically, so that it can send out 120 VAC at a certain amps rate exactly in that sine wave form. The amplifier is heavy-duty and expensive. A cheaper method is a synthetic "sine" wave that really is a switching circuit that can turn on voltage to various levels and then change to another level, so the series of voltage steps is similar to an sine wave at 60 Hz overall. This system is much simper to build, but the constant changes of voltage level involve VERY brief voltage fluctuations (SMALL spikes) that constitute high-frequency noise in the power, and some computer circuits cannot handle that well. A really good PSU should filter all that out, but some do not.
A major factor its switch-over time - that is, when the main supply fails, how long does it take for the PSU output to rise to a "normal" power level while the load experiences a brief Voltage sag? Low-cost systems charge the battery constantly but feed the load from the supply lines while monitoring them for failure. When the failure happens, then a conversion circuit kicks in to feed power to the output, but that takes several milliseconds. (ONE sine wave period in a 60 Hz supply is 16.7 ms.) A more expensive design charges the battery all the time, but always runs the conversion circuit from that battery to provide all the power. So when the main supply fails the load keeps on getting the SAME power it had - no sags.
Output power rating is important, and I find confusing. UPS specs always specify that in VA. We are familiar with the idea that power in WATTS is the product of Volts times Amps. But UPS's are different from an engineering view, so the VA rating is always substantially more than the Watts your load needs - the number for VA could be 50% higher than the Watts.
TIME of maintaining power is vital, and not all UPS makers tell you much detail. Further, as you might expect, the time the UPS can keep on providing all the power your load needs varies according to just how high that load is, and of course on the size and rating of the UPS. So at very minimum the UPS specs should tell the the time it can keep up power at a typical Watts load use rate. Telling you the max Watts with NO time spec is useless. The best makers will show you several specs of times for different Watts consumption rates.
How to use the time specs? What you need depends on what you use your system for. If it is in constant use with people around who are trained to deal with a power failure, sustaining adequate power for 10 to 15 minutes will be lots of time for the people to recognize the outage and conduct an orderly shut-down of all nearby computers. If your system simply MUST keep working for a long time like an hour or more before it can be shut down, then you need a larger UPS system. Systems that can keep you running fully for a failure of MANY hours are quite rare because of expense.
A Voltage Regulator is much simpler and provides NO protection against outright failure of the supply. It IS useful if your supply is reliable but tends to have frequent sags or surges in it that disturb equipment.
A Surge Protector merely makes sure that any high-voltage spikes in the supply get cut down to small spikes that normal equipment can handle. The cheapest and simplest of these connect across the supply lines a device called a Metal Oxide Varstor or MOV. This device has a very high resistance so there is no real curent through them under most normal conditions But at some significantly higher voltage, even if only briefly, they break down and become VERY good conductors so they are almost a short cirtuit between wires and the spike of voltage gets cut down to very small. The problem is that this is a sacrificial act - the MOV is totally destroyed by this, so it "burns out" and can never repeat this feat. Unless you're a techniocal person with access to parts and tools, you cannot repair the unit and must replace it. The worst part here is that you may not know that this all has happened - the protection event may not be noticed. So you have a useless Surge Protector NOT doing its job and you don't know you have lost protection. There are other much more complex Surge Protection systems with heavy components and clever circuits that do NOT sacrifice themselves and keep on protecting you. But - no surprise - they are more expensive! And for both types you need to find out how many JOULES of energy they can deal with without allowing some major voltage through to reach your load - the higher the Joule rating the better.
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