Please consider purchasing a Corsiar CX430, CX500, CX500M, CX600, or CX600M... depending on the power requirements of the graphics card you intend on getting. The "M" suffixed power supplies are modular and offer better cable management and airflow. This series of PSUs are known to fit most HP consumer desktop computers, including your HP p6520y.
If you have any further questions, please don't hesitate to ask.
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