Your Aquadapter has nothing to do with the burning out of the microswitch in the pressure switch.
The same thing would have happened if you had a tap and would also probably happen if you didn't have any switch at all.
The reason why the contacts burn is that the pump cycles (on and off very quickly) as the pump is supplying more water than the brush is using. In the early days we had the same problem. In those days we used 1/2" hose and 3mm jets.
Williamson pumps recommend their new Varistream in those days that did away with the pressure switch and allowed us to reduce the water flow. Initially I refused to spend another £75.00 on an electronic controller, preferring to buy a pump that delivered 3.8lpm as opposed to the one we had that delivered 5.2lpm. I had hoped that the lower delivery pump would stop the cycling. It did reduce it, but not to the extent that I had envisaged.
Within a week I went back to Williamson's and ordered a new Varistream. I believe these electronic controllers were and are a great step foward in the window cleaning business although some don't agree.
Although I have a new Varistream as replacement part in my office, I would consider the new Spring analogue controller as a replacement rather than the digital. My findings on the new Varistream problems and work around have been well documented over the past 8 months or so.