A power supply labelled as 180 W will likely draw significantly less than full rated load during normal use. 180 W might represent the load with the CPU and GPU both pegged at maximum which few applications actually do besides benchmark suites.

As far as the post above about capacitor inrush charging current being the limiting element, that really depends on the specific power supply and time-current characteristic of the circuit breaker protecting the power outlet. There are a number of different circuit topologies used in computer power supplies and they won't necessarily all have a single large capacitor. The technique described doesn't sound dangerous but it won't necessarily work for everyone.