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Is it okay to connect a internal hard drive (IDE/SATA/SCSI) to an internal controller (e.g. on-board the motherboard) and supply the power via another power supply or an external unit like the one below:

Does it matter if the external power supply is grounded or not?

EDIT: I'm aware the power supply below is grounded. If both the computer's PSU and the external adapter are grounded to earth, I assume there wouldn't be any problems. The one I have isn't. I'm afraid that the floating ground might cause problems. Any ideas?

Power supply image

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SATA and SCSI are using low voltage differential signaling for data transmission, which means they should tolerate even high ground offsets. IDE/PATA doesn't use this, so it should be much more sensitive to bad ground.

That said, I would avoid doing this, or at least make sure everything is properly grounded.

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It's perfectly fine. I have a power brick just like that. Hard drives are not "smart" about their power. There is no communication between the hard drive and the power supply. Electricity is electricity in that regard.

There are legitimate concerns about "dirty" power. But there is nothing saying that a computer's power supply is inherently better or safer than the external brick you linked to. It's just more complex is all. The item in the picture you linked to is grounded. You can tell because of the three blades in the power connector that goes to the wall.

The only concern you need to worry about is making sure the drive is powered up before you turn the computer on. SATA drives support hot-plugging but some BIOSes do not. IDE does not support hot-plugging at all. You won't harm the drive or anything. It just may not work.

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    Just because there are 3 pins in a power plug or socket, it doesn't mean that they are all connected. The standard "kettle lead" has 3 pins to allow for earthing, and all three may be wired on the lead, but it doesn't follow that the earth pin in the power supply is connected to anything. I would certainly not expect it to be connected to 0V side of the output, but you can check with an Ohmmeter. The earth pin in a mains outlet is intended as a protective ground, to prevent electrocution from exposed metalwork, but it is not generally connected to either side of a power supply.
    – AFH
    Commented Jun 19, 2014 at 11:26

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