jeny:
(My analysis after Google: X2 capacitor, more than 400V rating. Am i right or wrong?)
An X or Y capacitor (also known as Safety Capacitor) is only for use as a EMI filter, not a general purpose snubber.
Safety rated capacitors are generally not sufficient for use "in series" applications, unless you get one that is made of paper or multi-section construction. A series application is where the cap is being used as a coupler.
X capacitors should only be used from Line to Line (Across the Line, like an "X") and Y capacitors should only be used from Line to Ground. (Y capacitors can also be used in across-the-line, but usually have too low of a capacitance in that case.)