Just got in from some testing! APC SMT1000RM2U line interactive UPS on "Normal" mode it will complain and switch to battery. However, you can choose from "Normal" "Reduced" and "Low" Sensitivity. Changing it to Reduced, it works fine. APC Generally tells you to do this when running on generator power anyway
Charging an Ecoflow Delta 2, with no other loads plugged in, it sees the 120v and kicks on the charging circuit, but then drops out, and tries again, similar to what the UPS was doing. However, if I plug in a resistive load such as a heat gun, it will charge without issue at full power (This seems to be common with Ecoflow's and non inverter generators)
The fact the UPS doesn't complain when on the reduced mode gives me hope that most things will work with no issue.
The big test is a cheaper cheap 120v LED light bulb, plugged in, even with the heat gun running, there is some minor flickering. Not like fully on and off, but just very slight variations in light output. These cheap LED bulbs I tried with are by far the worst for flickering, so it would be interesting to see if a quality bulb flickered
Frequency is rock steady right around 60hz no matter what I do, voltage as expected is kind of erratic. With the Ecoflow charging at 1200w and the heat gun on the other leg, I got a nice 120v exactly however
The real test will be my fridge, freezer and mini split AC's. If those work, we're in business. All computers etc probably wouldn't care about the power input anyway, however, they are all on double conversion UPS in the house, so thats of zero concern. I didn't test the double conversion UPS as it means running a cord all the way through the house, however if the line interactive UPS was fine, the double conversion will be
Next test I'll dig out a spare recessed HALO branded light and see if that flickers (Thats all the lights in my house!)
Some pictures from the test. That cracked fender bugs me every time, but I have a new set on the way
Light testing rig
Short video of testing the UPS. You can see the voltage is pretty low, however there is essentially ZERO load on the light tower at this time, the UPS draws around 150w max, there isn't that much stuff being powered by it. So pretty much worst case for power quality, but everything runs fine
Its line interactive, so its passing the power directly through to the devices, and all of the hardware worked fine as expected