Keyboard automatically pressing random keys when grid voltage changes but my pc and monitor is connected to UPS. If I run the pc on full battery mode, keyboard is fine.

I recently built a PC specs:

Processor: AMD Ryzen 3 3200G

Mobo: Asus A510MK

Ram: G.Skill 8gb DDR4

PSU: Zebronics 450W psu (i cheaped out)

Consistent 128 SSD, (i cheaped out), WD blue 250GB HDD

UPS: Atris 1000VA UPS (i cheaped out, instead of buying APS)

Monitor: Frontech 18.5 inch (consumes 21W) (I cheaped out)

Keyboard: Zebronics Keyboard MK2100 (i cheaped out)

Mouse: Zebronics Mouse (i cheaped out)

Cabinet: Frontech Silver series. (I cheaped out)

Whole build cost ₹22,815 ($268)

(My motherboard has 8 Pin cpu connector. But the PSU has only 4 Pin CPU connector, I just plugged it in on right side of the 8 pin, I asked on r/pcmastereace, r/pcbuild, they said it should be fine but not recommend doing it. Currently I don't have budget to buy new psu, I have Corsair 450w PSC at home I may put the Corsair in my new rig by next month)

Everything works fine, in my area recently there has been severe voltage drops and increases randomly, we complained it to the power supplier, still hasn't changed. But I have UPS with automatic voltage stabilizer, and battery backup for 600W.

Keyboard automatically pressing randome keys, or the keys that I pressed like a seconds before, automatic pressing repetitive, annoying, automatically opening vlc, screen snip, -,8,9,0 keys, volume reduce key too(the keyboard has extra keys for volume, browser, this pc etc). All of the happens only when the voltage fluctuates, if I turn off the power to the ups immediately, the ups goes to battery backup mode(my monitor goes black for 2 sec, but pc is fine), keyboard is normal, works fine no issues at all. But when I turn on the power to the PSU, when voltage fluctuates, keyboard starts doing its thing. I have been making a protocol for my study, that's why I built the pc in the first place, now this keyboard, voltage fluctuations really annoying and disrupting my work. I changed usb ports, tried on all of my ports no changes. If I connect the keyboard to the front IO of cabinet (I cheaped out here too, USB 2.0 slots) the problem is much worse the the back ports.

I thought this things happens because I cheaped out on keyboard, so I ordered new keyboard and mouse from Logitech, it's coming tomorrow.

I can't find any similar problem as me on the internet, I have been searching for couple of days. So guys help me with this, thank you so much. Help me finish my first ever study article.