Bear in mind, there will be losses at all stages. The 180 watt supply itself will have to convert from AC to regulated DC. My FW 60 watt power supply measures at 92-93% efficient, which is pretty darn good. If the 180 watt charger is similar, expect it to draw around 195 watts in order to supply 180. Then that 180 watts, delivered at 36V, will have to get converted in the laptop, resulting in some loss as well. That loss means that there won’t be the full 180 available for use by the computer. I don’t know how efficient that conversion process is.
Mostly, I just wanted to make sure people understand that a power supply rated to deliver 180 watts out, will draw a bit more than that. How much more will depend on its efficiency.