Capacitors have built in resistance called (esr) this with external resistances determines time constant. Capacitors cannot charge to 50% unless you develop a circuit to cause it to stop charging at 50%. Regardless of supply voltage all capacitors will charge to peak voltage of supply less esr. In switching circuits such as timers capacitors will charge to 67.7 % of supply I believe because of ac resistance or reactance. Interesting question though.
