UPS is an uninterruptible power supply. When the mains power fails, UPS can still supply power to the equipment for a period of time. The voltage regulator is just a pure voltage regulator and does not have any delay effect.
A voltage regulator, as its name implies, is a device that stabilizes the output voltage.
A UPS can also regulate voltage. UPS equipment usually provides protection against both overvoltage and undervoltage, but typical voltage regulators have a limited range.
The efficiency of the voltage regulator will be much higher than that of the UPS. That is, for the same load and the same power of the UPS and the voltage regulator, the power consumption of the voltage regulator itself is much smaller than that of the UPS itself.
Voltage stabilizers and UPS are different and cannot be confused