The 'bandlimited white noise source' is specified by white noise's Power Spectrum Density (PSD), which is Power per Unit Frequency (V^2/Hz, power is indicated by V^2 usually in circuit design). (It is termed as Noise Power in the setting, but it is actually Power Spectrum Density)
Suppose your smallest time step (or sample time) in your Simulink is dt, then the maximum frequency range you can get is 0 to 1/dt. Noise power is specified by V^2 = (Voltage_standard_deviation)^2 = Variance. If your simulation length is N (fixed time step solver), then your frequency resolution or Unit Frequency is Fs/N.
So, set PSD = (Voltage_std)^2 / (1/dt), and set SAMPLE time as dt, run Simulink, send white noise output to workspace (array), run std() to see Voltage_std that you just set.
Plot PSD
f = Fs*linspace(0,1,N)
semilogx(f, 20*log10(abs(fft(noise)))
By doing so, it is equivalent to using 'rand number generator' by setting the same VARIANCE and SAMPLE TIME.
