# How to calculate what wattage transformer to use for LED light strip

I am looking to purchase some LED light strips, and I have seen these:

7.5 Watt RGB LED Tape

They are 7.5w, and have 150 LED lights over a span of 5m and the website states that they are 12V. But I am not sure what transformer/driver to use for these lights. The QA section, below the product description mention:

" To work out what transformer you require this is quite simple. You take the amount of LED tape you have in metres and x this by the wattage of the LED tape you have, again per metre. For example 7m of 4.8w LED tape: 7 x 4.8w = 33.6w Therefore you would require a 60w transformer. "

So for 5 meter of 7.5watts the calculation is 5 x 7.5 = 37.5W The website has power transformers, but at 100W and 150W, and when I rang them they were out of stock and the prices for the transformers were about 3 times what I can see on ebay.

Firstly, can I use a transformer that is producing 40W which is just above the 37.5W that I need, instead of a 150W transformer that they sell and claim is compatible for this LED strip?

Here is one transformer, that looks equivalent to the one they sell, at a relatively affordable price:

This gives me 12v x 12.5A = 150W, but I can see a 15V x 10A, which also gives 150W. Which of these is suitable for me (as they both produce the same wattage, but have different Volts/Amps), and what do the different Amps and Volts mean?