No higher watt PSU will only draw current as much is needed. But higher watt PSUs usually have higher capacity caps and charging them at switch on would have a higher load. Also 1KVA UPS will only output 1000watts at 100% efficiency which is not possible. For 1000 watts you would need atleast 1.5KVA UPS to be safe. But why would anyone get a 1000 watt PSU in the first place. 550W is good enough for any personal system.If someone buys a 1000w psu, then will he need to buy a ups with a capacity if 1 kva or higher? Or will a normal 600va ups suffice?
Will a higher watt psu draw more current only when needed or it may pull more watts arbitrarily, thus putting more load on the ups and increasing energy usage?