MT500 voltage regulator effect is certainly not as good as the regulator, so you can have the utility input when the regulator in series in front of the MT500, and at this time the MT500 just play a role of an uninterruptible power supply, a little bit of a big talent.
If that's the case, I suggest you buy the Santak TG500 (without voltage regulator) which is a lot cheaper, or you can buy a Santak Orlande V600 alone, which has a regulated voltage range of (140-300) VA