if your power draw at the wall for your computer with the gpu connected is 205 watts , thats mean your card probably pulling around 130-140 watts at the wall.
You can check easy your pc power draw if you have a integrated graphics in the cpu. Start the pc without  your rx 580 and measure the power draw connect your rx 580 start mining and measure your power draw , the different between that 2 number is going to be the closest number for a real power draw for your gpu.

Usually a simple built pc , with ssd, cpu, 4-8GB of mem, no extra cooling fans on idle is pulling between 40-70 watts...