Here’s definitive info I found on on this (below). There are markings on the circuit board - abeit very tiny - look for the ‘+’ (with 16.5v next to it) and on the other terminal a ‘-‘ sign below it. You’ll need a magnifying glass to see them. >>
Check the GRUD, Ground/N/Neutral/Nagative/-v mark and Positive/Live/L/+ve/+v sign of the circuit board. In your cable the white colour is positive and black wire is negative. If there are no marks which is unlikely than use amp meter to check the polarity. Wrong polarity can damage the charging chip so do not just guess if not sure