Why my phone can only work with original charger and original battery and original USB cable?

[AC Question]

I have a weird samsung galaxy mega 6.3..It only accepts original charger,USB cable and battery...The other's phone are not like this..once i went to a shop who claims that they only sell original accessories and they were completely caught when they were finding charger for my phone...first they told my phone got problem...so i brought my old charger and my phone can charge using that charger but cannot charge with any so called original charger that the shop offered..it cost me a lot but the phone offer me an excellent browsing experience...I feel complete with it but dont understand why is it fussy...i m using it since 2013