I am using a computer PSU to power a 92 watt(12V 6A) peltier device.The PSU has a rating of 450W,it has got 2 rails of 12V ,one delivering 15A and another delivering 16A.However when I connected my peltier device the current drawn from these rails are not more than 1.6A ,is there a problem with the psu or am I wrong somewhere?
The power supply's job is to supply 12VDC regulated- it's up to the Peltier to draw enough current at that voltage.
Assuming your power supply voltage is actually 12V (and assuming that you have not put something in series like an ammeter that would excessively drop the voltage)-- so the voltage across the Peltier device is actually 12V +/- not much, the Peltier simply isn't drawing the current you think it should.
Perhaps the Peltier is designed to operate on a 13.8V automotive "12V".
Most computer PSUs have a single transformer which is pulsed at high frequency, with multiple output windings that produce several voltages. Regulation is achieved by varying the on/off ratio of the pulses (Pulse Width Modulation). Increased current draw makes an output voltage sag, so the PSU compensates by increasing the PWM ratio to keep the voltage (almost) constant. However if only one output is loaded down then the higher PWM ratio will cause voltages on the unloaded outputs to go up, eventually triggering the over-voltage protection circuit.
The easiest solution is to simply put enough load on the other outputs to keep their voltages down. Drawing 2-3A from the +5V output is usually enough to get at least 10A from the +12V output. You can use a 2Ω resistor, which draws 2.5A at 5V. It should be a wirewound type rated for 20W or higher, and remember that it's dissipating ~12.5W so it will get hot!