Power source for 12V PWM controlled light
For driving 12 Volt LED modules or LED strips, fairly inexpensive and really small / lightweight switching power supplies are available, specifically designed for LED supply. For instance, this one supports 8.1 Amperes at 12 Volts, good for driving up to 90-95 watts of LED strings. 

No additional "minimal load" needs to be attached to these power supplies, internal circuitry provides any minimal load needed for stability.

Also, these power supplies are designed to work with a constant load or a PWM switched load, with no special handling required. 

Another point to keep in mind is that 60 Watts of LED lighting provides far more light intensity to the eye than a corresponding wattage in incandescent or other conventional lighting technologies. Thus you may not need the wattage you envisage at the moment.