Most commercial switched mode power supplies in IT equipment intended for home or office use bear a label showing 100 to 240V AC.
In the UK, the nominal mains voltage is defined as 230V AC 50Hz, but the Ofgen allowable range is 216V to 253V. Where I am at the moment, out in the countryside, it's 246V. I have seen it at 256V (above the limit) before they changed the tap on the 11kV transformer in the field nearby at my request.
Earlier this year I was staying in a foreign hotel and the mains varied between 85V and 218V. I disconnected my laptop charger when the voltage dropped below 90V, to avoid possible over-current burnout.
In another hotel, some years ago, the town mains vanished due to load shedding and I heard the hotel diesel generator start up. A few seconds later all the light fittings in the room exploded in a shower of sparks. I checked the room voltage, 300V AC, then walked down and asked the staff to reduce the voltage to 240V.
Voltage regulators are common in many countries, to cope with huge variations in mains voltage. These are not short duration "spikes" lasting a few milli-seconds, but long term variations measured over minutes or hours as the load changes.
In large hotels, each room has a large voltage regulator weighing roughly 20kg (44lb) to protect the air conditioning unit on the wall. You don't need a UPS to protect an ACU, but you do need something to offset the effect of huge voltage changes on the compressor.
You need a particularly robust UPS to cope with voltage swings well below 100V and above 260V, outside the range of most commercial units. A combination of a separate wide-ranging AVR plus a UPS might be applicable in Sri Lanka. I'd be inclined to ask a local engineer for advice.