The switch happens so fast in most modern UPS systems (10ms or less) which is fast enough for your PC, monitor and modem.
I have a 1,000 watt power supply along with 2 monitors, usb hub, modem, etc plugged into mine so went with a 1500VA / 900W model.
I don’t need it to power my sim for any length of time but just keep it running during those short power bumps. As well as protect it from surges.
The other advantage is it feeds your system consistent “clean” power.
This is the unit I went with.