some good information here, but I’d like to add some myself. don’t be fooled by what you think an UPS does. they are good to have, and can help protect your computer hardware and unsaved files, but they wont necessarily change the characteristics of your AC power. normally, an UPS will power a computer straight from the wall, using a relay inside it, which you can usually hear click if you listen for it. if power from the wall fails or the voltage dips low, the relay will click over and it’ll start using the battery to produce power and keep the computer running. the device you’re thinking of is called a power conditioner. it can be used as an UPS, with a built in battery as well, but the difference is there’s no relay, and it’s always producing its own clean sine wave power. basically, you could say you’re taking the DC from your battery banks, into the MSW inverter, converting to DC in the conditioner then back to AC a second time with a pure sine wave, and into the computer. power conditioners also have the down side of some power loss due to the conversions to DC and back to AC. simply put, save yourself time and money and get a PSW inverter, even a cheap one.
for my own use, I do plan on using a PSW inverter and an UPS for my desktop. I’m a programmer, so a desktop is important to me. there is a little extra power used by an UPS to keep the internal battery charged, but it’ll protect your computer from unstable power and allow you to shutdown properly. a laptop basically does this internally, because it has a battery, however it’s still possible a MSW inverter could harm the power supply for your laptop. these and wall warts can also overheat and burn out just like motors.
MrEnergy, your video has me thinking. when you’re testing on the bench, do you have a load on the inverter, or is only the oscilloscope connected? putting a small load on it may change the wave you’re seeing. it’s possible the squaring could be very low current. I don’t have as much knowledge of the internal workings as I’d like, but maybe it’s possible there are noise filters at the output of the inverter which are acting as tinny capacitors, and throwing off the scope. just a theory. try putting a 100 watt incandescent lamp on the inverter while testing it. let me know what you find.