Cpu low performance when plugged in

I have dell inspiron 7577 whenever i plugged in my charger i get low cpu speed its stuck in like 898 mhz it not always stuck at 898 but it also increases in like 1000+ but not stable..(also when in game)then when i unplugged the ac adapter and replug it solves the problem but just temporary i get 3.300+ mhz speed in cpu.. I want a permanent solution spent al ot of days finding solution but nothing works... I have set high performance already in power options
Pictures below
CPU when plugged in with ac adapter

https://imgur.com/a/qF6z2Ko

CPU when i unplug then re plugged the ac adapter again

https://imgur.com/a/BFnDOCT

https://imgur.com/a/EjQUrxO

Hope someone would help me solve this problem..