Electronic component unit and wire harness

A wire harness comprising:

• an electronic component unit provided in a power supply that is mounted on a vehicle and is capable of supplying power at a first voltage;
• and
• a power supply wire that supplies power from the electronic component unit to a device mounted on the vehicle, wherein
• the electronic component unit includes:
• a power supply terminal connected to the power supply,
• a circuit branch portion that is connected to the power supply terminal to branch power supplied from the power supply into a plurality of power supply systems, and
• a voltage converter that is provided in at least one of the plurality of power supply systems in the circuit branch portion, and converts a voltage of the power supplied from the power supply into a second voltage lower than the first voltage to output the second voltage.