Powering devices by USB is a murky, murky field with different hardware vendors outputting different USB currents and also requiring different USB currents for their stuff to work.
Personally, I'd triple check the connection of the disk drive to the laptop, and then get a compatible internal blu-ray drive. Laptop optical drives come in two thicknesses - 9mm high and 12mm high, and usually either ATA or SATA (often ATA up until recently) but the connectors can be different to what you expect.
If you give Dell your service tag they should be able to help you with a compatible drive. Alternatively buy a compatible one, and swap the fascia (should clip / screw on).