What is the output PEP of 500 volts peak-to-peak across a 50-ohm load?

Explication

500 V peak-to-peak is 250 V peak, which is 176.8 V RMS, and 176.8² / 50 = 625 watts. The 2500-watt distractor comes from using peak volts, and 5000 watts from using peak-to-peak volts, in the power formula.