Power Supply Options (for Straight Run and Centerfeed/Loop Back Layouts)
LED Light Strip power requirements are based on several factors, including the light strip layout and the length limitations of light strip-type lighting. 
And when choosing the transformer, we should have in mind that Transformer must be de-rated 20% to prevent overheating. And a big power transformer do no harm to the strip but good for safty. 

There are the following alternatives for the power supply:

up to 1.0m: 12V/0.5A (6W)
up to 2.0m: 12V/1.0A (12W)
up to 3.0m: 12V/1.25A (15W)
up to 4.0m: 12V/2.0A (24W)
up to 5.0m: 12V/2.5A (30)
up to 10m:  12V/5.0A (60W)
up to 20m:  12V/8.0A  (96W)
up to 100m: 12V/83A  (1000W, can use multi-source)

Step 1:  Calculate the power consumption of the strip you want

–We can calculate each strip’s power by knowing the LED Type and its rated power for each LED. The formula to calculate is Power Consumption = Wattage of each LED*LED QTY of strip Length. 

For example, for 100cm long SMD3528, 150LED/roll model, it’s 30LED per 100cm, so its power consumption is 30*0.08= 2.4Watt.

Step 2: Choose the appropriate type transformer

A: Non-waterproof transformer, wall plug in type , DC12V, from 1AMP (12watt) to 12AMP (120Watt)

Step 3: Select the Right AMP or Appropriate Quantity of transformer

The rule to choose transformer for strips is to give enough power . We can power several rolls of strip by one big enough transformer or by several pieces of transformer that can supply enough power.

Less power will do no harm to the strip, but jut without enough power, the strip cannot give out 100% of its brightness.

And when choose the transformer that we should to have in mind Transformer must be de-rated 20% to prevent overheating.

For example,

A:  If you ordered 1 reel SMD3528 with 300 LED (24 watt), you can use the 36Watt transformer.

B:  If you ordered 2 reel SMD5050 with 300LED (72Watt/roll, 2rolls total 0.24*600 = 144 watt), to power by one transformer to run, you can choose the 15AMP (180 watt); to power each row by one transformer, you can use 2pcs the 96Watt transformer, each roll by one 96watt.