Hp can i plug into a wall socket?

Hp bought new hp server,says warranty void if I plug into a wall socket !why not?what would happen?Since it has 2 redundant 800 watt power supplies,I’d need a ups of at least 1600 or better!
So…why can’t I plug it into a wall socket or power bar?
Stupid setup!backup idea is great,but having to have a ups to boot server is stupid!ps having to have a “reputation”to ask a question is stupid!