My PC has 450w PSU but consuming 117.9w to 122w while Im using the web lang. The extra wattage will be used when its at full load - thats why our PSU are called switching power supply because it fluctuate its current depending on the usage of the PC
take for instance the rig of bakkwakwak during the rig show at robinsons cybergate, at idle, its running at around 300w but when i played crysis, it went up to 630w power consumption