well theoretically the cable was rated for 6a at 250v equal to 1500w capable cord... (660w on 110v)
if that label is true...
can you check how much the power drain from the psu.. it should be on the psu manual book..
example: mine 750w bronze capable of draining tops 900w from power lines...
edit: if more efficient psu is more lower the difference (750w vs 900w),
and the actual power used depends on your usage and rigs..
mine in normal usage tops 450w that include, monitor, speaker, pumps, etc....
according my UPS software..