After putting a power meter (watt-meter) on my PC I found about 35 watts was quiescent, reaching up to 50 watts for youtube, but I got a big surprise drawing about 350 watts running TRAINZ, mostly used by my RX580 vidcard, pushing my old power supply to its limit. This Cool Master 550 watt unit gives me plenty of safety margin, with the modular bonus of minimal leads in the case - as I only run M.2 not sata storage.