I went off the power supply maximum output. 5.1 volts, 3 amps, so 15 watts per hour. 24hrs per day, 365 days a year, so 131,400 watt-hours, or 131kilowatt-hours. My electricity is about $0.25/kwh (advertised at 0.09/kwh, but when you add on bullshit fees, the final rate is much higher), so I came up with $32.85 as the maximum amount any device connected to that power supply could cost.