So here it goes,after looking out hundreds of pages regarding powering of Raspberry Pi 3B+ still some hesitations here.
I have totally read this out very detailed & nicely written answer by Milliways & official Raspberry Pi documentation along with many Reddit post. I came to know that i can use any power adapter of any output current rating provided that it ( adapter) capable delivering constant 5 Volts(±0.25V) supply.
As Raspberry Pi itself will draw only amount of current it needs from adapter as long as voltage provided to board is constant as standard input rating.
So my concern is can i go for power adapter which can deliver 3.4 Ampere or Qualcomm QC 3.0 capable( as it can deliver 5V-3A or 9V-1.6V or 12V-1.2A) as Raspberry Pi capable of handling current value.