Don’t think that all that glitters is only gold. It’s really a false proffecy. A decent power supply will present a very low impedance to anything but low frequency AC (50/60Hz). Now, think about how a voltage divider works. It drops voltage proportionally over the impedances of each of the elements in the circuit. If our power supply is built to be a low impedance to anything but power line frequency, then what happens if we put a power cord on it with an equal or lower impedance to non-powerline frequencies? Yeah. So keep that skinny 18 gauge cord on your low power devices because it’s the place where you want to leave the non-powerline noise frequencies behind at, before the power supply. So, that’s when cheap power cords can be good, when your power supply has a decent noise filter from the company that designed your hifi component.