How efficient is this power supply in terms of energy consumption, and does it have any certification like 80 PLUS?

The power supply has an efficiency of 70% minimum at full load.

Does this power supply unit come with all necessary cables, including SATA and Molex connectors, or do I need to purchase them separately?

Yes, the power supply unit comes with SATA and Molex connectors as part of its connectors.

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400W 400 Watt ATX Computer PC System Power Supply PSU Unit SATA Molex 24 pin New

CONNECTORS: 2 Peripheral, 1 Floppy, 2 SATA connectors, and 1 ATX12V P4 (Square 4 pin connector),1 x 20/24 pin main board connector (work on both 20 pin and 24 pin motherboard)
MTBF 100,000 hrs at ambient conditions Efficiency 70% Min. at full load Overvoltage Protection On all outputs Shortage Protection On all outputs Cooling Ball bearing Noise Level Maximum of 32db at 100% system loading
Built-in voltage overload protection Voltage switch for 115/230V AC input Support all Intel and AMD Complies with Intel AMD ATX specification
Safety Approved and warranty Approved by UL, TUV, RU & CE 1 Year warranty