If you want to make fudge using more than one kettle at a time, you need to use the same kettle model

Why? For consistency. Fudge coming out of two different types of kettles won’t look the same, especially if the voltage on each kettle is different. A 120-volt kettle heats fudge from 120 to 140 degrees Fahrenheit (50 to 60 degrees Celsius) and a 240-volt kettle can heat between 150 and 155 degrees Fahrenheit (65 to 68 degrees Celsius). That means the fudge coming out of the hotter kettle will pour out thinner.