Difference between external hard drive with power supply and without it

[finme]

Hello,
I would like to know if it's better to buy an external hard drive without power supply, the hd wil het power fromthe usb port.

 

[RealBeast]

Both work fine, but if you want a larger faster 3.5 inch drive you need an external power supply. The smaller 2.5 inch externals will work off USB power. Not really a better question, just one of what you need in terms of drive size and form factor.