Are you sure that the main breaker in your home supports 450W and not 4500W? Since what you're saying doesn't sound right. E.g electrical water kettles alone range between 1000W and 2000W. Also, electricity sockets are rated between 2000W and 5000W.
As far as PSU goes, here i need to know your full system specs.
And for UPS, your budget and location is needed (e.g USA, Europe, Asia etc).