Therefore, for voltage source, as +ve current direction is from + to -, the current coming out from voltage source is -ve. In Qspice, when you place a current probe at voltage source Vnnn, waveform viewer in default give you -I(Vnnn). But other spice program may give you +I(Vnnn) and you have to change it to -ve in waveform window.
Based on this principal, a common skill in spice is to use 0V voltage source for current measurement. Here is an example
Third party mosfet current measurement - QSPICE - Qorvo Tech Forum