App note from KEMET about the decreasing value of capacitance with respect to its rated value. Link is here
There are a couple of reasons why the capacitance value marked on the device you have, may not read anywhere near that value in the circuit application in which it is intended. The two major contributors to this are the capacitance roll-off with increased frequency exhibited by electrolytic capacitors, and voltage sensitivity (both ac and dc voltages) of capacitance associated with ferroelectric dielectric ceramic capacitors.
This topic has been discussed in previous papers. This paper is a culmination of many of those papers in order to provide a summary for the reader.