Harmonics in power lines are primarily generated by electronic devices, particularly switch-mode power supplies (SMPS), which create noise at their switching frequencies rather than the fundamental powerline frequency. Power factor correction capacitors can also contribute to harmonics if they are not designed for specific conditions, as their impedance varies with frequency. The discussion highlights the importance of understanding the relationship between power factor and load types, noting that inductive loads can benefit from capacitance to improve power factor. Additionally, the conversation emphasizes the need to differentiate between harmonics at the powerline frequency and those generated by electronic equipment. Overall, the effects of harmonics can lead to inefficiencies and potential issues in power systems.