Update=Resolved=  Restored Windows' from a system restore point and the problem disappeared.
I noticed something was off when the default thermal profile ("balanced") selected on Alienware Command Center was showing basically only two possible fan speeds for both the CPU and the GPU: 0% for both or 47% for CPU and 48% for GPU.Sometimes both fan speeds would rapidly go to around 50% and then go back to either of the static values mentioned above. There was absolutely no in-betweens, and the CPU could be reaching more than 80°C sometimes and fans wouldn't speed up at all (if they weren't completely turned off at 0%). So I created a new custom thermal profile and managed to solve the problem, now the fans wouldn't turn off and would increase/decrease its speed according to CPU/GPU temps. Now the CPU's temperature wouldn't reach more than 50°C on idle, which is what I wanted. It worked pretty well until today.As soon as I turned my laptop on the fans were going really fast, and it was because the CPU temp was being shown as around 80°C on idle. I'm pretty sure this is just plain wrong, the laptop wasn't even noticeable warm and this was very different from the numbers I was getting yesterday, so the temperature was being shown incorrectly for the CPU (GPU was normal). I tried using HWMonitor to check if it was a software bug and it's detecting the same crazy CPU temps, so I believe it might have to do with the core temperature sensors. I just updated my BIOS to 1.5.0 and it didn't solve the issue. What should I do? Edit: I forgot to mention, my laptop is less than a week old.  
Dell G15 5515 Ryzen Edition - Incorrect CPU temperature readings