External Linear PSU for Router - Voltage/Amps?

A technical question to aid in my rudimentary understanding of voltage and output.  How do I best match a replacement PSU to the wall wart voltage and amp output of my specific router -  a Netgear Orbi RBR 750 with specs showing 12V , 3.5 A DC ouptut.  I understand the 12V part but when viewing listings ( new/used ), I am finding most are showing amps above 3.5 with varying voltage.  

For instance a Teddy Pardo listing is showing a 15V 2A, and a TeraDak listing is showing 12V with either a 4A or 12A option.  How close to I stay to the V and A in my decision making?   I am looking to simply "clean" upstream a bit and wanted to start with a linear psu thats a reasonable $ amount ( $250 - $400) . Next step will be to add a switch.  Already have a solid ethernet cable ( Network Accoustics ) and streamer ( Aurender N200)  Also any recommendations on specific brands would help me out.