Actually I have those for quite some time now. I run them at a very light load for two reasons: this test can run for up to 2 hours and at light loads I noticed that the majority of PSUS featuring LLC resonant converters usually have the highest EMI spikes. So I apply a load of 28W. The most significant part is though, that I don't use a passive load (e.g. resistors) but an active load which simulates the response of a real system, meaning that it also generates EMI noise which the PSU's corresponding filter has to deal with, else it passes to the spectrum analyzer.
The standard dictates the 150KHz - 30MHz range, yes. The background noise is minimal, since I have a LISN and a 1:1 transformer behind the LISN and a dedicated AC line.