On modern drives you can see what the max amp draw will be from the label (at least on branded ones) like this:

Mine is a smaller laptop drive, and i know it does not pull more than 300mA at any load.

The image above i posted is a frame from a video i made while the disk was doing random read, and i took the frame that has highest current draw.

Larger disks can use much more power, so it will depend on your use case. A 3A adapter is more than enough for a full size spinning hdd. 2A is more than enough for a small laptop drive, sdd or usb stick.

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