QNAP TS-459U-RP Turbo NAS Reviewhardnrg -
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A single 150W PSU can power the entire unit with all four bays populated with hard drives. So why would you need more than one? Having a second PSU allows the unit to continue to operate in the event of a PSU failure. The QNAP TS-459U comes in two versions, the SP (single PSU) and the RP (redundant PSUs), so you could always get the SP and decide whether or not to add a second PSU at a later date. If your data is irreplaceable (or mission critical), having redundant PSUs is one of the fail safes you should be using.
Each PSU has two round LEDs: the green one lights up if the PSU is running correctly, and the red one if it isn't. The square red button is to stop the audible alarm triggered by a PSU failure.
The knurled thumb-screw and swing-up handle allow the PSUs to be removed and installed without tools.
Spinning the PSU around, a golden finger edge connector reveals how the PSU can be inserted and removed without cables. These industrial PSUs are branded as iEi, and are manufactured by ICP Electronics.
Each PSU has a 40mm Sunon fan that can blow 7.7 CFM at 21 dB(A) when running at full speed.
To satisfy your curiosity (and mine), I opened up a PSU to take a look inside. You can see a sensible heatsink/airflow design and all high-quality components such as electrolytic capacitors by Nippon Chemi-con and ICs by Power Integrations.