A food shop has become more expensive since confinement started (I'm abroad).
To stop people from shopping too frequently and to create more space in the shop for social distancing, they seem to be selling only the larger quantities. e.g. 1kg of minced beef whereas before you could also buy 300g or 500g. Also I've noticed that some brands aren't available, e.g. you have to buy Heinz ketchup instead of a cheaper brand.
Secondly I've bought booze at the supermarket, which I don't do otherwise as I go out for a drink once a week or so in a bar with friends. I've bought "treats" too like the odd bar of chocolate or ingredients to bake a cake, which I don't do usually.
Thirdly, I buy things like shampoo, face masks, candles in the supermarket as the other shops where I'd buy those things are closed.
Also more money on cleaning products, I wouldn't say I've 'gone mad' but am certainly using more of them - part of that is from being home more often. (Has anyone else noticed the toilet roll getting used up much faster as you are never going to the toilet outside the house nowadays?)
Another thing is that I do like to have a few staples in the house, more than before, so I am adding an extra tin or two of chickpeas, lentils, tomatoes, tuna, etc. to my fortnightly shop.
However, as other posters have said, quite a few of these additional costs are offset by spending nothing on eating or drinking out (or transport to get to and from bars and restaurants), nothing on clothes, and less on things like make-up, books...
OP, are you eating all of the food that your DP buys? If you are having to throw away food (or stockpiling excessive amounts of dried or frozen food), then yes he is buying too much.