The orange LED DS9 illuminates when the SCU35 board is connected to a valid 9-20 V, 3A (min) USB-C power supply. See Board Power System for details on the onboard power system.
The following figure shows the USB-C Power Delivery (PD) Sink Controller (U34). Power (9-20 V DC) is applied to the board via the USB-C connector (J28 not shown) and input to the sink controller on the VBUS and VBUS_IN pins. As long as the input power is valid, it is passed to the PPHV output pins to provide the main power system voltage. The ADCIN [x] pins strap the configuration settings for minimum voltage input, maximum voltage input, operating current, and maximum current. For more information see the datasheet for the TPS25730D device at the TI website.