There’s no real standard. This year we got our red/black zip cord and Anderson connectors from Powerwerx, our PWM/sensor wire from servocity, and Dupont (PWM) connectors from Pololu. We source automotive terminals locally.
We use wire from Home-Depot. The only thing that should vary between wire of the same gauge is the way the wire its self is made, (solid core or stranded) and the insulation, other than that the AWG system keeps things standardized.
This is precisely why we have stopped using wire from the Home Depot and Lowes. Solid core wire (e.g. THHN) is great for applications that don’t move, like houses and other buildings, and is easy to bend to a sharp angle and keep organized, but it tends to fatigue failure (breaking) on systems which flex or vibrate like … robots. If you want to source wire locally (e.g. I need to get this working TONIGHT), go to your local Pep Boys, O’Reilly, Auto Zone, etc.
Solid wires also do not work as well with Weidmuller connectors on the PDP or the spring connectors on many of the control system pieces as stranded.