PC Causing Power Fluctuations

[DragonSlayerXD]

I Recently Built A New Pc, It Worked Fine For About A Month. But After That It Started Creating Power Fluctuations Whenever It Runs On My Home UPS Or PC Backup UPS. It Runs Fine When On Mains. The Fluctuations Only Occur Whenever The Pc Is IDLE Or While Doing Light Work Like Web Browsing, Watching Video Etc. But When I Stress My CPU Or Play Some Games The Fluctuations Disappear. I Thought This Problem Was Due To My Power Supply So I asked Cooler Master To Replace My PSU. But Replacing The PSU Didn't Help. Does Anyone Has An Idea About The Cause Of The Power Fluctuation.

My Pc Specs:

OS: Windows 10 64bit

Processor: Intel i5 6500

Motherboard: Asus Maximus VIII Hero-BIOS 3101

PSU: CM B500

HDD: WD Blue 1 TB

[knightslugger]

shitty wiring in the house? POS UPS?

[DragonSlayerXD]

I don't Hav any Problem With my Other Pc's. Only this One Creates Fluctuations.