The proper article for the phrase depends on the context of your sentence. In general English usage:
A is a critical internal hardware component that converts high-voltage alternating current (AC) from a wall outlet into low-voltage direct current (DC) usable by a computer's sensitive electronics. Beyond just providing power, a high-quality PSU acts as a safeguard, regulating voltage to protect components like the CPU and GPU from power surges or fluctuations. Key Specifications to Know How PC Power Supplies Work - Computer | HowStuffWorks COMPUTER POWER SUPPLY
is used when referring to any non-specific unit or introducing the concept for the first time (e.g., "A computer power supply converts AC to DC"). The proper article for the phrase depends on
is used when referring to a specific unit already mentioned or the unique one inside a particular machine (e.g., "The computer power supply is found in the corner of the case"). What is a Computer Power Supply? Key Specifications to Know How PC Power Supplies