I am clear that negative currents are simply currents that flow in the opposite direction. I am unsure as to how to apply this information to the real world. (relating to positive and negative leads)
For reference, my power supply has a negative voltage terminal.
For conventional current in the passive sign convention, current still flows out of the more positive and into the less positive terminal regardless of whether the supply is positive or negative. In otherwords, in a positive supply it flows from +V to 0V. In a negative supply it flows from 0V to -V.
If you reversed the current, it would go from being a source to a load as per the passive sign convention.
If ground level was 0V, below ground levels were negative voltages, and above ground levels were positive voltages, it doesn't matter if you are on a floor above ground or below ground; When you drop a rock, it still falls down to convert gravitational potential energy to kinetic energy. Reversing the current specifically for negative sources would be like making it so in a basement floor a rock has to drop up to do the same process.
I believe a drawing often says more than a thousand words, so:
simulate this circuit – Schematic created using CircuitLab
I have indicated the voltages, 5 V is just an example.
The arrows indicate the direction of the current assuming the current has a positive value.
And indeed, at the + 5 V terminal the current flows out of the supply.
While at the -5 V terminal, the current flows into the supply.
If your power supply is providing a negative voltage, and if that supply is actually providing power to the circuit, then conventional current will be entering the negative voltage terminal.
Whether this current is positive or negative depends on how you describe the direction of the current.
If the power supply was able to both sink and source current (like an ideal voltage source) then there are circumstances where it could either provide power to the circuit or absorb power from the circuit. In other words, the supply can act like an active load. That's why it is important to stipulate the actual power of the power supply.
What direction does current flow? It’s all about your point of view… from a point in your circuit.
Kirchhoff’s Current Law tells us that currents flowing into a point are regarded as positive, while currents flowing out of a point are considered negative.
What determines the current direction of flow is the potential difference (voltage) between that current’s origin, and the point we’re looking at:
So a negative supply, with respect to ground will have current flowing into it, while ground will have an equal current flowing out.
KCL also tells us that the sum of all the positive currents vs. the sum of all the negative currents are equal. That is, the same current flows out of a point in a circuit as flows in. Add up all the currents, positive and negative, and you should get zero.
