All regulated APV's have an amp limit, no matter what you set the V or W to they will not output a power level that exceeds this limit.
Some automatically reduce the power output to a level that equals the amp limit, some set an error code & refuse to fire until the power is reduced manually.
6v / 1.5 = 24w & 4a
14.978w / 1.5 = 4.75v & 3.16a