A preheating power supply , comprising: power conversion circuitry including first and second output power connectors of the preheating power supply wherein the first output power connector is connectable to a second output power connector of a different power supply , wherein both the first and second output power connectors are connectable to a first contact tip , and wherein the power conversion circuitry is configured to output welding-type power to the first contact tip via the first output power connector and the second output power connector ; wherein said preheating power supply establishes a preheat current path via the first contact tip configured to return to the preheating power supply via the second output power connector of the different power supply ; being characterised in that : the preheating power supply comprises a bypass path prevention circuit comprising one or more switching elements and a controller , and in that : the controller controls the bypass path prevention circuit to: enable the one or more switching elements to conduct current when less than a threshold weld current is detected as flowing between the first and second output power connectors ; and conversely when more than a threshold weld current is flowing between the first and second output power connectors . power conversion circuitry including first and second output power connectors of the preheating power supply wherein the first output power connector is connectable to a second output power connector of a different power supply , wherein both the first and second output power connectors are connectable to a first contact tip , and wherein the power conversion circuitry is configured to output welding-type power to the first contact tip via the first output power connector and the second output power connector ; wherein said preheating power supply establishes a preheat current path via the first contact tip configured to return to the preheating power supply via the second output power connector of the different power supply ; being characterised in that : the preheating power supply comprises a bypass path prevention circuit comprising one or more switching elements and a controller , and in that : the controller controls the bypass path prevention circuit to: enable the one or more switching elements to conduct current when less than a threshold weld current is detected as flowing between the first and second output power connectors ; and conversely when more than a threshold weld current is flowing between the first and second output power connectors . the preheating power supply comprises a bypass path prevention circuit comprising one or more switching elements and a controller , and in that : the controller controls the bypass path prevention circuit to: enable the one or more switching elements to conduct current when less than a threshold weld current is detected as flowing between the first and second output power connectors ; and conversely when more than a threshold weld current is flowing between the first and second output power connectors . enable the one or more switching elements to conduct current when less than a threshold weld current is detected as flowing between the first and second output power connectors ; and conversely when more than a threshold weld current is flowing between the first and second output power connectors . <EOS>