Help needed working out the size needed for a power supply

[badwolf84]

Hey guys,

I'm currently rebuilding my NAS built from a Raspberry Pi and 3 external HDD. The NAS side of things works well, slow as crap but suites my needs. Using a Pi because its what I had laying around and I had the external HDD spare. It's Just annoying when I need 4 power points to run everything, so I'm wanting to replace them with a Power Supply. 

I'm not sure on what size power supply I need. the 12v wall adaptors are all rated to 1A,and the Pi is supplied with 5V@2A.(using a buck converter for the 5v needed for the Pi http://www.ebay.com.au/itm/191731851020 ).   My research suggests 20w max during power up for each USB HDD and 10w for the Pi. So my maths suggests a 12v 6A 70w Power Supply . If someone could check my figures, before I release the magic blue smoke along with all my data, that would be awesome.

I was thinking of using one of these power supply  http://www.ebay.com.au/itm/AC-110-220V-TO-DC-12V-24V-Regulated-Transformer-Power-Supply-For-LED-Strip-Light-/400469998223 or if you have a recommended supplier let me know.