Suitable connector/wire for 3A output from PSU
There are two factors that determine the wire thickness for an application these are:-


Ampnicity. Is the wire thick enough not to catch fire when you put that much current through it. In this case you are ok.
Voltage drop. This is a function of wire resistance and length. As you are only dealing with a few inches you are ok here as well.


The equivalence of other wires from different manufacturers has been covered by @PlasmaHH in his comment. If it has the same area of copper you are ok. You do have to take into account the quality of the insulation for ampnicity and this may be an issue with some foreign manufactured wire. However you are well inside the safe zone for this.