Thank you for your answer, I'm a bit disappointed by those connexion issues.
I'm using PowerApps on line, not in Visual Studio :
is it the reason why I don't see 'enter custom value' choice on the bottom ?
When I make my formular, I insert an object 'Data table'
which I connect to the Oracle connector, selecting a whatever table (one of the firsts table of my database).
Then for this Data table inserted on my window, I select 'Advanced' properties.
For 'Data Items', I change the value for '[TEST].[PART_TAB]'.
==> It doesn't worked : I have an error 'Invalid name'
Do you try also connexions on other tables than the firsts given in the list ?