Developing a power supply is harder than it looks.  The commercial ones output 12V which drops significantly by the time it reaches the strip.  There are multiple, random LED strips with different voltages.  Multiple voltage droppers for a single laptop power supply would be the easiest way.  After considering how to drop multiple voltages with the cheapest microcontrollers, Mike Harrison introduced a PWM generator based on 2 op amps.  1 op amp generates a triangle wave.  The other op amp is a comparator that chops the triangle wave into PWM.  It could be far simpler than a microcontroller.

LTSpice showed it can work, but it requires higher speed op-amps which are only in surface mount.  The trick with LTSpice was arranging the power supplies exactly as shown.  A single supply or a -5V supply didn't work.  It would actually take more parts than a single microcontroller.