For a long run between my 12V solar panels and the charge controller I ordered some 10 gauge stranded wire to handle future supply currents. The red jacketed stuff in the image below is what I received from a random seller on eBay:
The wire in the middle is silicone jacketed genuine 12ga (black) from W.S. Deans and on the right is silicone jacketed 10ga (white) from McMaster-Carr. Using a micrometer to measure I could possibly get what they sent to pass as 12ga but certainly not 10 as advertised. We all enjoy inexpensive supply chains originating in China but you simply can’t trust specs. It is the reality of things and why high end manufacturers implement acceptance qualifications on parts from suppliers.
I recommend this supplier for good wire. And be sure to bookmark and print out a useful site such as this for offline reference.
n.b. Technically these three examples are cable since they are comprised of a group of conductors insulated together in a single jacket. So keep that in your pocket for later.