The Gigabyte P550B is offered at a low price, and this is its main advantage. Apart from the low EMI emissions, the compact dimensions, and the correctly set OPP, there are no other major positives for this product. It seems like Gigabyte just took an outdated platform from MEIC and put its badge on it without taking the time to test it and tune it properly.
However, we are not even sure if several of this product's significant flaws can be fixed, given the platform's old design. Besides low overall performance and bottom low efficiency, especially with light loads, the fan speed profile is highly aggressive since it has to cool the low-quality caps. The bridge rectifier doesn't use a proper heat sink, and the quality of the FETs that MEIC used is questionable. We were surprised that this unit could survive our tests, but if we pushed it a little more, it would easily break, given that there is no over-temperature protection.
It is better to invest a bit more and get a decent performing power supply from Corsair (VS550 or CX550), Cooler Master (MWE 550 Bronze), XPG (Pylon 550), or Asus (TUF Gaming 550). To keep the cost as low as possible, Gigabyte dropped the build quality in this product to low levels, with performance following closely.
Group regulated power supplies are not ideal for today's PCs. It is better to invest in a PSU with DC-DC converters to generate the minor rails, which ensures that it won't have any issues with unbalanced, among the rails, loads. Most systems nowadays load the 12V rail and only lightly use the other rails unless they have many addressable RGB LED strips installed, which draw power from the 5V rail.
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Disclaimer: Aris Mpitziopoulos is Tom's Hardware's PSU reviewer. He is also the Chief Testing Engineer of Cybenetics and developed the Cybenetics certification methodologies apart from his role on Tom's Hardware. Neither Tom's Hardware nor its parent company, Future PLC, are financially involved with Cybenetics. Aris does not perform the actual certifications for Cybenetics.