|The USB port you plug the USB to hard drive adapter into must be able to supply the full USB spec 500ma.|
If you plug it into a USB port built into the laptop it may work fine.
Some laptops, e.g.some ACER models, cannot supply 500ma per USB port - they can only supply 500ma for two ports total, or for all the built in USB ports you can plug into, total.
In that case, the USB to hard drive adapter may work fine
- when it's the only thing plugged into the built in USB ports
- when you use a USB Y cable to plug it into two USB ports built into the laptop.
The same applies to external hard drives in an external enclosure.
On the other hand, some bioses DO NOT recognize USB to hard drive adapters.
External hard drives in an external enclosure are recognized by any bios.