As stated in the title my PC suddenly completely shuts down as if i would lose power. I am pretty sure that it is the Power supply but i wanted to ask if it even is possible for a CPU or GPU to just let the whole computer lose electricity before i buy a new PSU
Have you monitored the temperature at all? If it shuts off after 1.5 hours of gaming, that sounds more of a heat issue than power. It sounds like maybe a lack of thermal paste.
Get something like CoreTemp and monitor your CPU temps while gaming.