Kill A Watt reports 2.5 amps but with a power factor of 0.4
A power factor of 0.4 means that only 40% of the power being drawn is usable (real) power. That would support your observation of drawing more than twice the current expected. 

What PC power supply are you currently using? Depending on what you're currently using, it might be worth upgrading to a higher quality unit with better PFC and efficiency.