## 4 Results of Measurements
It can be seen that the highest energy efficiency value was obtained for the dedicated charging system loaded with Smartphone for an SoC level equal to 70% and was as high as 99.6%. In contrast, the lowest energy efficiency value was obtained for the tested system loaded with Notebook for an SoC level equal to 10% and was only 81.5%. It can also be seen that the value of the PF for the tested system loaded with Notebook was an increasing function for the whole range of variations in the SoC level battery; its highest value was equal to 0.73 for an SoC level equal to 90%, and the value of energy efficiency at the same level of SoC was the highest at \(\eta\) = 92.5%. The characteristics shown in Figures 5-7 prove that the battery charge state practically does not affect the input current value, but an increase in the SoC value results in a significant decrease in the output current value. The values of the THDI and THDV parameters change only slightly, by a maximum of 3%, in the entire range of changes in the SoC value. It is also worth noting that the energy efficiency of the charging system under consideration increases with an increase in the SoC value and reaches a value equal to even 95%. Figures 8-10 show the effect of the SoC level of the batteries of selected mobile devices on the measured waveforms of input current I\({}_{\text{in}}\) and the spectrum of this current for the charging system loaded with two selected mobile devices. The waveforms of input current I\({}_{\text{in}}\) were measured for the RMS value of the power grid voltage V\({}_{\text{inRMS}}\) = 230 V and frequency f = 50 Hz. Two values of the SoC level equal to 10 and 90%, respectively, were selected for the experimental tests. The output voltage V\({}_{\text{out}}\) of the charging system depended on the mobile device currently being charged and took on values V\({}_{\text{out}}\) = 9 V (Smartphone) and V\({}_{\text{out}}\) = 20 V (Notebook). The dependence of the measured input current spectrum I\({}_{\text{in}}\) on the SoC level battery was presented as the ratio of the individual harmonics  
to the value of the fundamental harmonic amplitude of the supply current waveform. In the experimental study of input current spectrum I\({}_{\text{in}}\), both odd and even harmonics were presented. Figure 8 shows the waveforms of input current I\({}_{\text{in}}\) (a) and the input current spectrum (b) as a function of the SoC level of the built-in battery in the smartphone. The output voltage V\({}_{\text{out}}\) during the battery charging process was equal to approximately 9 V.  
Figure 8: Measured waveforms (**a**) and the spectrum (**b**) of the input current for different values of the SoC battery used in Smartphone. Figure 10: Measured waveforms (**a**) and the spectrum (**b**) of input current I\({}_{\text{in}}\) for different mobile devices at SoC = 50%. Figure 9: Measured waveforms (**a**) and the spectrum (**b**) of the input current for different values of the level of the SoC battery used in Notebook. Analyzing Figure 8a, it can be observed that the time waveforms of I\({}_{\text{in}}\) current are highly distorted and do not resemble sinusoidal waveforms regardless of the charge level of the selected mobile device. It should be noted that a higher peak-to-peak value of input current I\({}_{\text{in}}\) drawn from the power grid was obtained for SoC equal to 10% and was I\({}_{\text{inpp}}\) = 0.64 A, and a lower value of 0.48 A was obtained for SoC equal to 90%. The mentioned peak-to-peak value was equal to the difference between the maximum and minimum values of the considered waveform. Analyzing Figure 8b, it should be noted that regardless of the SoC level of the Smartphone battery, the spectrum of the input current waveform had large normalized harmonic values. For SoC equal to 90%, it can be noted that as many as nine harmonics of the fundamental frequency had the maximum amplitude.