Hello. I don't know of any Swiss studies on this topic. However, a number have been done in other countries.
The results of a much-cited study by Dun & Bradstreet showed that people spent 12-18% more when using cards to pay than they did when they used cash to pay.
A study by McDonalds in the US showed that customers spent around 65% more per purchase when they paid with cards compared to paying with cash ($7 average card purchase vs. $4.50 average cash purchase).
Results of a study by researchers at the Carnegie Mellon University in the US showed that people who primarily use cash and only occasionally use cards generally do not spend more when using cards, but people who primarily use cards to pay spend more on average for each purchase.
Another study by researchers at the Carnegie Mellon University found that paying in cash triggers pain receptors in the brain, but that paying by card does not trigger any sensors at all. In the words of the researchers, paying by card acts as an anesthetic for the pain of spending.
Research by an assistant professor at the University of Toronto Scarborough suggests that people value goods purchased in cash more than they value goods purchased by card.
It is worth noting that credit card companies including Visa and Mastercard openly advertise the fact that people spend more when paying by card to merchants whom they hope to win over to accepting card payments.
I hope this helps to answer your question.