When I put it back on though it was also on 200 Volts in stead of 220. I tried to put it back in 220 Volts, but it didn't work. Only after reading the manual I found out that it had to be on battery power before you can change this setting. Luckily I had a visitor of to buy my Moog Voyager RME and just before that I saved all my files. Also the storage units in the rack in my server room luckily are on a different UPS, so I didn't lose any data. After restoring everything I did some tests on the UPS and everything seemed fine, but it is still strange that this happened. Ah well it only cost me some time. When the battery is full I'll switch of the fuse again and see what happens. But this time I'll do that with less equipment on :)
The reason I run the studio on 220 Volts in stead of 240 Volts is that I have lots of old synthesizers. Some are even build in 1971. In those days the power wasn't as high as today and the power supplies in those machines are not designed to regulate that much power down. It is only a few percent, but it will shorten the life of the power supplies for sure. Well bad luck today, but the UPS has saved me a couple of times as well before.