In order to connect the lamp to a wired connection, a breakout is necessary. The USB power will cutoff if there is power on the 12v rail, to protect the computer motherboard.
The RJ11 CAN FD jack are compatible with DUET3.
The external FAN4 and FAN5 Micro Fit 3.0 connectors has 12v directly from PSU. The PWM signals are independently adjustable. A typical 120mm fan uses 0.5 amp at full power. The power connection for the external breakout is 9amp max.
The 4 pin header on the main shield is for wireless module UART (RX/TX) connection.