I bought this HD about a year ago and can give you the following answer:
Yes the mains plug of the HP HD power supply can be used with my Seagate 8TB. However, the HD requires 2 amps of current. So the HP power supply must have 2A or more. There are also HP power supplies with only 1.5A.
Additional note: The Seagate 8TB HD is extremely slow when writing a lot of very small files (clip art etc.) 50 - 300Kb/s. This is in contrast to other Seagates. This is in contrast to other Seagate HDs (e.g. 2.5 inch 4TB) or all other products from other manufacturers that I have used.

I also own them, but my 1.5a needs a