ST-550P-AM is a 550 W power supply from Seventeam where you can manually control the fan speed and can even disable it. Let's see if this unit can really deliver 550 W.

Here is a snippet:
"ST-550P-AM is a 550 W power supply from Seventeam where you can manually control the fan speed and can even disable it a feature called "ASM" by the manufacturer. We've already tested another model from Seventeam called ST-550P-AG which achieved a good performance for an entry-level model and we were curious to see if ST-550P-AM and ST-550P-AG are the same product (since they have similar model numbers) with only the addition of a fan control knob on ST-550P-AM or if they are completely different units. Let's see."



Link: HardwareSecrets