Question Pc underperforming I think

[Jibran tahir the gamer]

I have a core I5 8400 paired with a rx 580 8gb 16 gb of ram windows in a ssd gaming motherboard a normal 1 tb hard drive
But I am getting stuttering frame drops in fortnite not even in endgames even when I am fighting a person offspawn what could be the problem anyone can guide me somehow also my power supply is 600 watts I get about 200 fps in game I have a 75 hz monitor so cap the fps at 120 fps in fortnite
BTW in 1080p I tried stretch resolution as well still the same problem

 

[rgd1101]

cpu/gpu temp and usage during the game?
what the make and model of the psu?

 

[Jibran tahir the gamer]

Cpu usage is around 80 to 100 when in game and gpu usage is around 60 to 90 res 1600by900 if I play in 1080 p my cpu is at 100 and gpu is also on 100 but their is stuttering in 1080 p when I play fortnite
I donnot know the psu manufacture I do know it's a good one I have to check that I cannot do right now