Assuming you are talking analogue not digital.
The length of track makes absolutely no differance to what power supply is needed.
The type of motors you are using can make a differance to what power supply is needed.
The length of track makes a differance to what track wiring is needed and to how important it is to have good joints between every track section.
Extra wiring, sometimes called jumper wires or taps, can be a bit of a luxury on short tracks, but become more or less essential on longer the tracks