Power and Energy spectral densities of a linear system
The relationships, with $x$ the input voltage to the network, $y$ the output voltage from the network, $R$ the load resistance, $p(t)$ the instantaneous power dissipated at the load, and $E$ the energy dissipated at the load and $t_0=8$

$$Y(f)=H(f)X(f)\\
y(t)=\mathscr{F}^{-1}\{Y(f)\}\\
p(t)=\frac{y^2(t)}{R}\\E\bigg|_{t=0}^{t_0}=\int_0^{t_0}p(t)dt=\int_0^{t_0}\frac{y^2(t)}{R} dt$$

IF the cable or network is a lossless cable (!), the example turns trivial:
$$y(t)=x(t)\\
p(t)=\frac{x^2(t)}{R}\\
E\bigg|_{t=0}^{t_0}=\int_0^{t_0}\frac{x^2(t)}{R} dt$$