There are various way to load data into Simulink environment as mentioned in the following link:
What is important to understand is the fact that Simulink is a time based modeling platform which means you perform some simulation over a range of time values. It makes sense to import freuqency and power spectrum data in Simulink if with each time step you have a different set of frequencies and corresponding power spectrum to analyze.
However, if it is just a single frequency and corresponding power spectrum vector and you wish to perform some calculations on this dataset it does not make sense to use Simulink. For that you can import the data into MATLAB and do whatever operations required.
Hope that helps!
