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I need to power up 4 peltier elements (at 12vdc, approx 50W) and 2 fans( at 12vdc).
I was wondering whether a charger(like that of a laptop/mobile) that supplies 12vdc for a single device will power all of these devices up if I connect them in parallel?
If not what kind of device (preferably cheap) should I go for powering these devices?
At 12 V DC, 50 W means that it will draw 50 / 12 = 4.17 A. Multiply by 4 and you get almost 17 A. Let's provide 1 A for both fans. This means you'll need a power source that can supply 12 V at 18 A (a total of 216 W output power).
A laptop charger usually supplies 19 V at 3 to 5 A. So it is useless.
If you can get one, a computer PSU may be good for this. Just make sure the current on the 12 V rail is greater than 18 A and add a dummy load (resistor) on the 5 V rail to get it working.
Another solution is to buy from your favorite electronics parts supplier a SMPS kit with those ratings (12 V @ 18 A output).
As Cornelius has pointed out, a typical charger simply does not have the current you need, but other options exist. eBay is a good source of power supplies. You can get what you need for ~ $20 (US). Also note that, depending on what's available in the way of power supplies, you can connect your elements in combinations of serial/parallel, to use either 12 volts/16 amps, 24 volts/8 amps, or 48 volts/4 amps. I'm ignoring the fan loads here, although I would strongly recommend a fan per element, total 4 rather than the 2 you have specified.
That said, you may not be able to drive your elements with a full 12 volts. Unless you have a proper heatsink on your cooler, with proper airflow, the Peltier will overheat and may self-destruct. So make sure you have a temperature sensor on the hot side of your elements, with the circuitry to cut off your power supply if the element gets too hot.
