The Dell Poweredge R710 can hold up to 2 power supplies. The spare power supplies come in 570W 870W options. Make sure you are replacing or adding an additional power supply that matches the wattage of the current power supply installed. Always replace with a genuine Dell power supply specifically engineered for the Dell Poweredge R710.
If you are receiving the error message Dell Poweredge R710 power required exceeds PSU wattage you should look at installing the largest wattage power supplies. If you are currently using the largest wattage Poweredge R710 power supply you will want to try replacing them. One of the power supplies could be causing the Poweredge R710 to have a wattage error.