The extention is just that, it extends the one outlet into 2 outlets. They are only controlled by the DC8 outlet.
It is the same as if you got a extention cord that had 2 or more plugs in it.
If the DC8 plug is on then both extention plugs are on
If the DC8 plug is off then both extention plugs are off.
Cheaper to go to harbor frieght (or local tool shop) and buy an extention cord with more than one outlet in it.