Pc Power Supply Estimator -

You never want to run a Power Supply at 100% capacity.

PSUs are most efficient at roughly 50% load . Operating at 100% capacity constantly generates excessive heat and can shorten the lifespan of the unit. pc power supply estimator

Look for an 80+ Rating (Bronze, Gold, or Platinum). You never want to run a Power Supply at 100% capacity

But if you buy a 550W unit, you might be in for random shutdowns, coil whine, or a dead PC a year from now. pc power supply estimator