Building a rig based on Geekom mini pc and Im starting to consider if I need a UPS.
Can anyone recommend one they use. Starting to wonder if I should have gone down a laptop route!
I’m using an Eaton 3S 550 to run my Lenovo mini PC, a tablet charger and also my Roland Fantom 07 on the battery protected sockets… the non-battery sockets run my 2 Alto TS408 floor wedges.
I use this one
Line-interactive is the keyword in your selection 
I have all my keyboards, laptop, audio I/f, WiFi, switch, mixer, wireless receivers and IEM connected.
No power problems anymore (even disoriented Guitar/bass players or drummers are now able to unplug power without shutting down all these system 
)
Are you planning on using that as your main and only power source, or are you going to use this to make the stage dummy proof (as @tripleB suggests)?
Providing power for a few minutes is not too difficult. Providing power for a 3 hour performance is a whole other story.
Eaton and APC are brands that spring to mind. The weight is at least linear with time of battery autonomy you need.
I use this with my mini pc on festivals - it keeps it running for 1.5 hrs
I don’t quite understand: do you mean that you use it for 1.5 hrs powered by the mains without a mains power cut?
How long can it power your appliances in the event of a mains power cut?
Just a few minutes…to avoid rebooting pc after short power glitch.
Then you’ve a lot of choice. I would always buy one that’s bigger than I need, to compensate for decreasing performance over time (especially the batteries will deteriorate).
So I basically want a small one for just a few minutes to fit in rack case and cover power glitches.
The problem is those things are very heavy
Can power my mini pc rig for 1.5 hrs on ups battery alone
Buying one that’s too small after some time, is still heavy. They’re alway too heavy 
Yes great idea for a UPS. Funny story: we use to play this small club and our power would trip in the last set. I had a UPS so all was ok with me. After our stage power tripped a few times, we traced it back to a portable pizza oven that was in the kitchen on the same circuit. Late at night… ordering a frozen pizza from the bar was a common thing.
…from the trenches, LOL 
This one weighs less than 6 lbs. and dimensions are 10” X 5.5” X 4.1”.
I’ve always used these live. Have replaced a few over the years (using them for over 10 years, 150+ shows a year) but they are solid and keep my equipment from turning off when there are minor power interruptions.
CyberPower ST425