When evaluating a PSU, the most critical factor is Wattage and Rail Distribution. Ensure the continuous power output meets the system requirements, with a strong focus on the +12V rail capacity, as this powers the CPU and GPU. Additionally, prioritize 80 PLUS Certification (Bronze, Gold, or Platinum) to ensure energy efficiency and reduced heat generation. For high-end builds, look for Full Modular cabling to improve airflow and aesthetics, and verify the use of 105°C-rated Japanese capacitors for long-term reliability and stability.