A power supply comprises at least one transformer that is placed around an active power line and is connected through at least one power conditioning system to provide a conditioned power source for at least one electronic device. Power is generated by scavenging power from the power being supplied on the power line. An asset-monitoring apparatus comprises a sensor package in communication with a monitoring system and a power supply that generates power for the sensor package, the power supply including a transformer placed close to the power line powering the asset being monitored and a power conditioning system that conditions the power supply for use by the sensor package. An optional energy storage device may receive power from the power conditioning system and provide primary or backup power for the sensor package or other electronic device.