This will probably be easy:
I'm building a 3d printer, and I currently have a 360W power supply hooked up to my arduino which is hooked up to ramps 1.4 (http://reprap.org/mediawiki/images/6/6d/Rampswire14.svg). The problem is that my heat bed is draining too much energy. (like after a minute of operation, the led's go off)
Anyway, I thought I might solve the solution by hooking up the power supply to a smaller power supply (its actually a 100W 12 V laptop charger) in parallel. I think it would work, but I want to make sure that there is a small to no risk of frying my electronics.
Will it work? :)
Short answer no, you will fry stuff. The two PSU will not be matched and will fight, one pulling up, one pulling down. Best case you can combine them with low impedance balancing resistors but that's not really a good way for mismatched units and is less efficient. In your case you should find a bigger PSU or split up the loads to different supplies if possible.
Actually it depends on the power supply - some will fight, others will simply fail to co-operate (the slightly higher voltage one will do all the work). In general connecting PSUs in series or parallel will not work - they are not like batteries in this respect.
Use a separate supply for the heaters (connect the grounds of the supplies together though). Use transistors on the outputs to operate the heaters. If you aren't using PWM, you can use relays instead if you wish.