The power supply is unsafe when used with the adapter for Australia or New Zealand. The hard drive/SSD and USB cables are not affected. There is a risk of electric shock arising from the exposure of live parts if the power supply is assembled incorrectly.
What to do...
Stop using your power supply (APP524-051240U), turn off at the wall before unplugging and store it somewhere secure. Contact Western Digital to oragnise a replacement power supply. In the meantime, you can continue to use the hard drive/SSD without the power supply (with the USB cable only).