It uses the same convention for sources and loads, which is that + power is absorbing and - power is delivering.
Since the voltage is positive the current is negative to give you a negative power.
If you switched it up for loads and sources you'd just get confused by sources that are really sinking and such...
If it really bothers you you can double click the plot and add a - sign in front of I(xxx)
The 'plus' terminal of a resistor isn't shown on the schematic so you have no good way of knowing which direction the current actually is.
If you don't know you can check out the voltages, those must be correct.
If the direction keeps bothering you you can rotate the resistor and even though it looks identical on the schematic it will reverse the displayed current direction.
The current in R1 is 1 mA, and the current in R2 is 10 mA, it does show the correct current in the component. The only iffy part is the direction.
I am sure there is a simple way to change the directionb of that arrow but for now here is an amplifier circuit. You can't learn transistors without an amplifier circuit.
Gosh darn it confused me again.
I have to save to the desktop or it won't upload.
Anyways, hope this is useful.
I posted a Transistor Amp using a single supply before.
Here is a Bridge Amp. With any bridge the emitter resisters can tell you a lot. Check currents R1 and R2 with the output Resistor Current. You can see because the peaks don't match that the output is out of balance.
The output is also low compared to the 2V input because I used bigger emitter resistors than anyone would want if they were building for power output. But since the design is only using small transistors it would be better to increase the size of those emitter resistors or just add an output series resistor to reduce the currents and power output.
I think you wanted to see a single transistor used in a double ended supply The trick I can think of that would make that useful is balancing the output to ground and I think that is trickier with a single Transistor. I will have to think about an example for that.
And for anyone, please feel free to point out anything that has information value, but don't pick on my poor Bridge Circuit too much. I was trying to make something simple and sane at midnight in a few minutes so I can go to sleep. It is just a demo and a few flaws like the ones I pointed out might actually make it a better demonstrator.
I am also wondering if you are looking for a circuit that works with just one voltage source. In the first Amps I add examples for that is actually two amps, or more accurately two version of the same Amp. The second Amp I just removed the emitter Bias Resistor and bypass capacitor.
If you do a frequency response curve you will see that it was causing some loss of gain and phase delay at frequencies below KHz, but it prevents some distortion.
The two amps are a copy including the voltage supply which is not really needed twice. Both amps could have used the same voltage.
And there is another voltage - the signal source. An amplifier typically needs some AC to play with.