RCCD tripping but subsequently found the problem

[Kevin51]

I am diyer retired mecahical engineer so not a sparkie. My son/gf bought a portable A/C a few weeks back due to the heat. It was bought from a reputable supplier. Called me today did I have any fuses. Yes I have spare fuses, why do you want a fuse. The A/C keeps tripping out the flat. Explained it wasn't the fuse but as the A/C is brand new didn't think that was the problem. Suggested they tried it in another flat and see if it trips there.
I was just registering here to ask suggestions when I got a call back from my son. They solved the problem, for some reason today they plugged it into an "adapter" for some reason not directly into the socket. I told them to throw the adapter away.
But just to satisfy my curiosity, the A/C is going to pull a lot of power so not a good idea to run it through a shared adapter but could it be that two lower power devices would not trip the supply due to a fault with the adapter and running an A/C crosses the threshold and trips the supply?
I would have though even one or two low power devices should trip the supply or did they by plugging in the A/C just blow the adapter up?

 

[plugsandsparks]

The other devices in the adapter could have been class 2 devices and the a/c class 1. A portable a/c does not really pull that much power, but yes i have come across faulty adapters so good call to ditch it.