If i switched off the server remotely ... can i switch on remotely ?
no change will happen at Physical connection ( power)
Physical or virtual machine? For the former Dell idrac or HP ILo could work. For the latter you can do via the hypervisor.
It really depends on what you want to do.
One common way to remotely turn on your is through Wake-on-Lan but this required your network driver support it and you could send specific package to turn on your PC.
In case you want to use Wake-on-Lan be careful of configuration and make sure setup your network to only allow this feature from authorized users.