Dell U2422H 23.8" 16:9 IPS Monitor - Manual (Page 47)

Setting Up the Monitor
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47
Connecting the Monitor for USB-C Multi-Stream Transport (MST)
Function
A PC is connected to two monitors in an initially OFF power state, and the PC
system power state is in sync with Monitor 1 power button. When you press
Monitor 1 or PC power button, both Monitor 1 and PC turns ON. Meanwhile,
Monitor 2 will remain OFF. You need to manually press the power button on Monitor
2 to turn it ON.
Similarly, a PC is connected to two monitors in an initially ON power state, and the
PC system power state is in sync with Monitor 1 power button. When you press
Monitor 1 or PC power button, both Monitor 1 and PC turns OFF. Meanwhile,
Monitor 2 will be in Standby mode. You need to manually press the power button on
Monitor 2 to turn it OFF.