Expanding on that: in competitive electricity markets, in theory, total demand is met by the cheapest plants (by "marginal price": how much does an additional unit of electricity cost?) that are available.
The marginal price of PV, wind and hydropower is pretty much zero.
The next cheapest are usually older nuclear fission plants and coal power plants.
Then is a huge gap and then come newer nuclear plants and gas fired power plants.
But all of these plants aren't built over night. So maybe before all of the datacenters, total demand may have mostly been met by renewables and coal and gas power plants only operated a few hundred hours per year. Now, total demand rises and those plants need to operate more often. That's why the prices rise just because of demand increase. Other effects (e.g. changes in regulation, corporate greed, ...) might be at play as well.
"Claimed by someone saying they were a left-wing extremist group." - fify
Someone else claiming to be the same group distanced themselves from the attack and there are important clues pointing to the original post claiming the attack was written in Russian and machine-translated into German.