Never size UPS tightly.
You can't be sure if transfer to battery operation would be succesfull when nearing specified max load.
There's time delay before UPS starts providing output voltage and during that time power supplies of PC and monitor are drawing power from their primary/bulk capacitor.
And once input voltage returns power supply likely draws higher surge to recharge that capacitance.
(from cold start that surge is decimal position higher than nominal current draw)
Also you can be sure that battery size is minimal and UPS likely won't take battery aging/wearing well possibly degrading actual available output power fast in few years.
Higher than mandatory size UPS has more battery capacity and aging/wear of it doesn't form problem risk as fast.
If you want to use normal main power plugs instead of getting IEC connector power cables there aren't that many possibilities.
Like some APCs, Cyberpower BRIC has UK sockets.
The UPS adopts CyberPower's patented GreenPower UPS™ technology to enhance UPS operating efficiency, reduce heat generation, consume less power and save more energy costs than conventional UPS models.
www.cyberpower.com
Unlike APCs Back-UPS, those are line-interactive.
AVR functionality does some voltage regulating, like correct smaller brownouts without need to transfer to battery.
Also they have faster transfer time to battery operation, because there's no mechanical switch between inverter and load.
There are three topologies of UPS systems: offline vs line-interactive vs online. What are their differences and how to choose the right UPS system for your design? This article will make a comparison among these three designs in four aspects: operating principles; functions; benefits and...
community.fs.com
For offline/standby and line-interactive consumer UPSes that doesn't really matter, because power draw on UPS control circuitry doesn't grow with its output
