How much power is lost at each adapter connection. Ex: From a Temp power construction power source where an adapter is plugged in directly, then to a Y, then to another Y, and then to multiple extension cords?

Have to know the length and gauge of cords used.

Chuck

If nothing is plugged in then nothing is lost...
The losses will be dependent on the cords used (as Chuck pointed out) and the
Amount of power connected to the cords known to many as I squared R losses due to the inherent resistance of the cables...
Typically, these losses are small unless of course your cords are a hundred feet long and/or the load is large...