i have several Antminer S9's and a problem with my electricity which is voltage drops and the machines keep restarting. So my question is can i add a not so big UPS on each and every miner NOT to keep it running on power drop but to clear any peaks on the electricity
What you might be able to use, instead of a large expensive UPS, is an AVR, or automatic voltage regulator.
Not sure if you're running on 110V or 220V, but I know Tripp-Lite and APC make them (sometimes also called a "line conditioner"). I have an APC line conditioner I use on some home theater gear, and some cheaper no-name AVR's I use on other TVs around the house, since I also have trouble with low voltage conditions at times.
These don't use a battery, but rather a transformer with a variable tap. So when the voltage drops (or increases) beyond a set point, you'll hear it click and it adjusts itself to either boost or reduce the voltage as-needed.
They're cheaper than a UPS and you can get large ones that could handle an S9.