Capacitance, C, of the capacitor is its capacity to be charged with the charge Q, in coulombs per volt of the applied voltage U. Formula:
C=Q/U

Reactance, reactive resistance, Xc:
Xc=1/(2*pi*f*C)=1/(6.2832*f*C)

Energy which can be stored in capacitor in joule or Ws:
E=(1/2)*C*U*U
C in farad, U in volts, E in joules.

Charging and discharging time:
t=R*C

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EMI suppression capacitors class X (X1, X2), Y (Y2):
X capacitor is connected terminal to terminal while class Y capacitor is connected terminal to accesible parts (protective earth/ground). According to SEMCO 201-1978 standards max 125VAC may be applied to Y capacitor. X1 capacitor is used between live and neutral in fixed installations. X2 is used between live and neutral in plug connections. Y2 capacitor is connected from live and neutral to earth and must threfore have extra safety.