That is true for ceramic capacitors like X7R, X5R and Y5V.
There is a loss of capacitance as the voltage increases. For the
X7R and X5R the tolerance is around 30% at the rated voltage.
For Y5V the tolerance is around 80%.
Using an X7R at 40% or 50% of its rating gives you essentially
a flat capacitance (which is a tighter tolerance). For ceramic
caps I try to stick to X5R and X7R (for caps 1000pF and up).
If I use a Y5V are I will typically double or triple the voltage rating.
For ceramic capacitors take a look at the dielectric datasheets at
Kemet.
(* jcl *)
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