how do work transparencies in tga files?

I was trying to modify something in Bordinstrumente_1.7 in psCS2

but when I resaved the tga file, the alpha don't seems to kick in.

All the items are square with all the background in black
Saved in 24bits and 32 bits later, no RLE... I'm getting this:




I reopened the file and the Alpha channel was still there

what went wrong