How much current is being drawn from the DCC booster? It isn't obvious, until its current limit trips. It isn't easy to measure, because it is an AC current. But there is a product that measures it, called the Ramp Meter.
The ramp meter sits in the power feed from the booster to the railway. It reports two things: the rail voltage (13.7v here); and the current drawn (0.14A here).
On my railway, it tells me what I'd suspected: that the current drawn is tiny. Typically I see half an amp max with two trains running at that end of the railway. When the picture was taken there was nothing running: 0.14A is the current "lost" in resistor wheelsets and static load of the DCC decoders.