Here is the only reliable way to find your PSU wattage, along with a few workarounds if you can’t open your PC case.
Input your CPU, GPU, and number of fans. It will recommend a wattage, which usually matches the "standard" build for those specs.
Software like , CPU-Z , or Speccy will not show your PSU wattage. However, you can estimate the minimum PSU you need based on your components, then infer that your existing PSU is at least that large.