This Tripp Lite unit has two features that modern PCs users will find somewhere between very useful and almost mandatory. It’s a line-interactive UPS with pure sine wave output.

A square wave IS a summation of sine waves, in the same sense that 12 is the product of 2*2*3. Yes, there are other ways to describe 12. It’s 10+2, or 36/3, or the square root of 144, among ...