Knife switches are still in common use today, theres nothing "old tech" about them. The entire purpose of that switch is simply to disconnect power to the machine completely so that the electrical system can be worked on. The purpose of the fuses inside are the same as a circuit breaker or fuse box, to prevent the machine from drawing too much power. All that being said, the power should come from the wall, into the knife switch/orange fuse box, then go to the converter, then to the motor.
"I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."