hello.
i’m looking for a small UPS unit for my network equipment.
requirements:
i don’t need much capacity, 500 Wh is more than enough.
any recommendations for what to buy, and where? thanks.
Any. That meet your power requirements that work with NUT:
(NUT has a generic USB driver that should work with most but to be sure just look at thier site.)
This may be an unreasonable limitation, most electronic devices these days using switching for power regulation.
Yes, as Nathan advised, anything NUT compatible should be fine. It is a well established industry standard. Let your capacity requirements be your guide. Remember you may not need to keep hardware like display monitors alive during outages, but networking equipment may be vital to stay up for security and alert requirements.
You forgot to mention if you are paying in roubles or shekels… 
Inverter/chargers are standard equipment in boats and RVs. You have some “house” batteries which run all your loads when you’re not plugged in. The inverter automatically takes over if the AC power is unplugged. Basically a DIY UPS. And of course when mains power is available again, it switches back and charges the batteries.
You can size the battery bank however you like. Lithium is a good choice these days if you can keep them at a temperature they like. Or, on the low end, a bank of 2 or 4 golf cart batteries are inexpensive and reliable.
I have no idea how the cost of this setup compares to a dedicated UPS, and it’s probably not as pretty. But it’s robust and can be sized for almost any requirement.
Hi,
I use this UPS for my systems and computer: APC Back-UPS Pro 700. ( https://www.se.com/us/en/product/BR700G/apc-backups-pro-700va-420w-tower-120v-6x-nema-515r-outlets-avr-lcd-user-replaceable-battery/ ) Hope this helps! 
“anything NUT compatible should be fine”
so the question is, how do i know if a unit is NUT compatible? i don’t remember reading anything about NUT compatibility in the descriptions.
Check it against the database that Nathan linked to