Each of the three voltages is perfectly stable. There is no orange or red in the diagram while yellow (denoting a deflection within 2-3% from the nominal value) can only be seen in the area of minimum or maximum loads. This is a sure indication of independent voltage regulation although it is not listed among the official features of the Purepower series at the Thermaltake website.
The output voltage ripple is within the norm: about 35 millivolts on the +5V and +3.3V rails (the allowable maximum is 50 millivolts) and about 50 millivolts on the +12V rail (the allowable maximum is 120 millivolts).
The PSU employs a Yate Loon D14BM-12 fan remarked as Thermaltake TT-1425B. This 140x140x25mm fan has a rated speed of 1400rpm, according to the Yate Loon website, but I’ve got doubts about that. Describing the PSU at its own website, Thermaltake says “1900rpm Fan Inside.” Anyway, it’s not the rated speed proper but the efficient regulation depending on load or temperature that is important.
The fan is half-covered by a piece of celluloid film that drives airflow back into the rear part of the case. This is a questionable solution since it reduces fan performance almost by half. The film may also rattle irritatingly if not fastened properly (I had this problem in one PSU where the screws were not tightened to the end).
The fan speed remained constant at 1000rpm until a 200W load. Then it began to grow up quickly until reached 1800rpm at a load of 475W. This must be the rated speed of the fan because it didn’t change after that while the temperature of the exhausted air was growing up. I don’t quite grasp the idea of this regulation. Why make the fan work at maximum speed when the load is not yet the highest? Perhaps the developer hopes that no one will use this PSU at its max load.
So, the Purepower RX 550 AP is an average model in terms of noise. It is not silent, but quite acceptable for a majority of users.
The PSU is 85% efficient under typical loads and its efficiency goes down to 83% at full load. The power factor is over 0.95 as you can expect from a PSU with active PFC.
The Purepower RX 550 AP (W0150) is a high-wattage power supply suitable for SLI or CrossFire systems, let alone systems with a single graphics card. It has good electrical parameters and works rather quietly. It is not exactly quiet despite its large 14cm fan and is inferior to the PSUs from Zalman, Seasonic and Cooler Master in this respect.