Decipher this capacitor's label?
That is an X-type safety capacitor).  

Printed on the side:

MKP/SH: denotes polypropylene film dielectric, self-healing

B32921:  denotes the case size; this case size is typically rated 305VAC.

40/105/56: Climatic Code from IEC 60068-1, interpreted as follows, obtained from here


  CLIMATIC CATEGORY The  climatic  category  indicates  the  climatic 
  conditions   which   the   capacitor   may   be   operated.
  According   to    IEC 60068-1 the climatic category is expressed by a
  three  group coding e.g. 55/100/56.
  -  The first group indicates the lower category temperature  (- 55 °C).
  -  The   second   group   the   upper   category   temperature    (+ 100 °C).
  -  The third group indicates th e number of days (56) which  the  capacitor  can  withstand  within  specified  limits  if   exposed to
  a relative humidity of 95 % and a temperature  of + 40 °C.


I suspect if you can view the rest of the component markings you will find the capacitance, tolerance, and probably the voltage.