cproaudio:
Thanks for the advice, for the moment I'll stick to my DC-AC converter simply because it's functioning

and because I have 300W available. More then 150W doesn't exists in DC-DC converters or is very expensive. Don't you thing a VGA is a little bit too big?
Gutter :
I bought the "blackbox" from a local electronic store. According to them, it comes from Velleman.