On most G/Vboxes, the maximum momentary current draw is 3 or 4 amps and the voltage drops significantly under load. Quite typical for these units to output 15-20Vdc at 2amps under load.
You will often see "liberties" and "marketing embellishments" with specifications. Often when the manufacturer is asked for the product specification, the reply is, "what do you want us to print?"