A 750 Watt power supply unit would provide ample power for the new graphics card, the existing system, and any additional LED lighting and cooling accessories. This offers headroom beyond the minimum recommendation of 650 Watts from the graphics card manufacturer, which is beneficial for future upgrades and ensures consistent power delivery even under load. A 500 Watt PSU would not meet the recommended minimum and may cause instability, while an 850 Watt supply may provide more power than needed, increasing cost without offering tangible benefits for the current configuration. A 1000 Watt PSU would significantly exceed the requirements and would be more suited for a system with multiple high-end graphics cards or more demanding components.