Upman have stated that the SDS200 requires a maximum of 750mA which is 9watt at 12volt. And he also stated that the SDS100 charge the 3,7volt battery with 700mA.
If the SDS100 runs for 8 hours from a 5400mA battery it will drain a constant 675mA which is 2,4watt. That's almost 1/4 of what the SDS200 requires. Add the 700mA charge current for the SDS100 battery and it will be a total of 1375mA that are needed from a power supply. It's good practice to have some overhead to not stress the power supply at full capacity, so the 45% overhead up to 2000mA seems logical.
/Ubbe
If so, why not include this information in the manual?