The 1kOhm is the load R. Which means those terminals are to be used as the DC source. The 100uF Capacitor is meant to smooth out fluctuations of the DC.
The fluctuations of the DC source are still visible with the Voltmeter (as it focuses on the AC, eliminating the offset). These are small enough to be negligible on the main graph though.
I find pretty neat the way current vs voltage is represented.
