Difference between power spectral density, spectral power and power ratios
I have no idea what your calculation of power spectral density gives since
I cannot understand it.

If a signal $x(t)$ has Fourier transform $X(f)$, its power spectral density
is $|X(f)|^2 = S_X(f)$.  The absolute spectral power in the band of frequencies from $f_0$ Hz to $f_1$ Hz is 
the total power in that band of frequencies, that is, the total power 
delivered at the output of an ideal (unit gain) bandpass filter
that passes all frequencies from $f_0$ Hz to $f_1$ Hz and stops everything
else.  Thus,
$$\text{Absolute Spectral Power in Band} 
= \int_{-f_1}^{-f_0} S_X(f)\,\mathrm df + \int_{f_0}^{f_1} S_X(f)\,\mathrm df.$$
The relative spectral power measures the ratio of the total power in the band 
(i.e., absolute spectral power)
to the total power in the signal.  Thus,
$$\text{Relative Spectral Power in Band} 
=  \frac{\displaystyle\int_{-f_1}^{-f_0} S_X(f)\,\mathrm df 
+ \int_{f_0}^{f_1} S_X(f)\,\mathrm df}{\displaystyle\int_{-\infty}^{\infty} S_X(f)\,\mathrm df}.$$