I was looking at it from a different perspective. Regardless of the output power, N3U doesn't have to depend on the external source power since it has a built-in internal battery. While a dongle like Woo Tube-mini will have to draw power from a source. Now, if Woo Tube-mini has a max spec of 1W @ 8ohm, then P=V*I=R*(I^2) => I = SQRT (P/R) = 354mA. These are ideal case paper calculations without accounting for losses due to heat dissipation, voltage drop through USB cable, the efficiency of various components, etc., all of which can drive the actual current draw from your smartphone closer to 390mA (assuming a 10% increase). Again, lots of assumption goes into this, but from what I have seen while testing other dongles and monitoring the current draw of the USB port, based on their max spec the current draw doesn't change too much when you use IEMs with either lower or higher impedance. But anyway, I don't want to get off the main topic of N3U