can I use US servers in Europe?

The Dell R200 has a 100 - 240V auto-sensing power supply. This means you can use the server anywhere in Europe (with the correct power plug). Just plug it in and it will adjust automatically to the voltage.

The amp usage will be approximately the half of your current amp usage in the US. Because the power usage of your server will be the same and P = U * I (Power = Volt * Current).

"345W" in the Dell spec sheet means the power supply can handle a maximum power usage of 345W. This has nothing to do with the average power usage of your server. The average power your server uses depends on the hardware (CPU, Disks, etc..) in the server and the server load. A server which is handling 1000 requests/min uses more power than a server which handles 10 requests/day.

The only way to know the power usage is by measuring. Maybe your current colocater is already measuring the power usage of your server, so you could ask them. You could also guess your servers power usage by Googling power usage of other comparable servers under comparable load.

If you want to have a safe guess you can divide 345W by the voltage. So 345/230=1.5A. This is the maximum amp. Your server will not use more than this. Your server will likely on average use less, because most power supplies can handle more power than the server requires. And your server will not be under full load 100% of the time.

This Dell document says that the power supplies are auto-sensing so they should be safe moving from the USA to the Europe.