Certain SSDs have an ugly high peak consumption (average powermeters will not show) and as per the specs USB3 consumers are allowed to draw up to 900mA @ 5V as such with two USB3-A receptacles 9W need to be reserved for potential USB consumers (+5W for two USB2 ports).
That’s the whole reasoning for Radxa providing a 30W PSU: peripherals that need to be optionally powered in addition to the board itself.
How should such thing exist? USB-C knows two power modes that do not rely on PD and that’s 5V at either 1.5A or 3A (7.5W or 15W). USB PD defines modes above 15W.
And what most consumers don’t know: powering with 5V is a sh*t show in general since many power bricks are simply crap and only with ultra short cables and thick wires the voltage sag can be avoided. Details in this thread: Rock 5B power through GPIO pins - #27 by tkaiser