A PC's power supply unit, or PSU, takes AC power from the wall and converts it into DC power for your PC's components. During this conversion, some power is lost and is exhausted as heat. If a power supply is more efficient, it requires less AC power to produce the same amount of DC power than a less efficient unit and less heat is produced.

Most PSUs have an efficiency range of 80% to 96%, which changes depending on the amount of power being used (load), and the quality of parts like transistors and capacitors inside the PSU.

If a power supply has an 80% efficiency rating, it can deliver 80% of the power it takes from the outlet to your PC components, while the other 20% is lost as heat.

Any Electricity that ends up being wasted as heat from the AC to DC conversion can affect your electric bill. Additionally the PSU is going to have to cool itself more and that is going to reflect with increased fan noise from the PSU. When choosing a PSU, you should consider the efficiency of the unit as it affects power consumption and noise during long gaming sessions.