What is the opposite of the Power Supply Rejection Ratio?
What you are expecting is never shown as this is the product of the spectral density of the load current times the spectral density of the source impedance. 

Vs(f)= I(f)*Zs(f)

It is more useful to examine impedance ratios, Q and f-3dB and use a filter simulator to examine problems.  I have found this way to be very effective ( Falstad's filter+Bode plots) for component selection and effects of ESR on various C values with CLC Pi filters to attenuate and improve decoupling with both differential for conducted noise and CM chokes for radiated noise.

At DC this reduces to simply DC impedance ratio source/load which is also known as Load Regulation error which is often in the 1% range.  

In the audio frequency range , the inverse of this is called damping ratio referred to a standard load speaker/ source impedance with closed loop gain.