Kudos to Voodoo for finding a real world answer. I thought the most relevant quote form Voodoo’s link to the question that stated this thread is below:
So AlexXXL With enderTown’s example, I would say that you could barely power your 120 HDDs with two 1200 watt server quality PSUs. I would go with two 1500 watt server quality PSUs to be safe and solid. This also assumes that you a safe wiring setup
If you do go with another 100 HDDs I would add two more 1500 watt PSUs and spread the power equally.