Are there such thing as powerful charts? If so, what’s a powerful chart?

That phrase is used by astrologers, but in the end it is often a value judgment.  See below.  A powerful chart could come about several ways.  One is to have many planets in their rulership or exaltation and those planets ruling the angles and/or in them, or some of them.  Another way is to have those planets really well placed, say in the MC or ASC.  

A powerful planet is one that is in a good sign (for that planet), above the horizon, direct in motion, swift (i.e. travelling faster than it's average speed in its orbit), in a good house or being angular, not applying to an unfavorable aspect with the malefics and applying to a favorable aspect to the benefics.  It might be impossible for a planet to have all of the favorable conditions in one chart (or unfavorable), but having a few of them,  makes a planet powerful.

That being said, I'll cite two charts that make us go Hmmmmm.  General George S Patton has a weak chart by any standard, and he accomplished quite a bit with his life.  He had a lot to overcome.  At the other extreme I have a chart in my files of a man who has almost every planet in strong dignity and let's be kind and say he hasn't done much with his life up to this point. The strength or weakness shows how difficult or easy things can be, but it is up to the individual to overcome or set a direction and work with the chart to have a successful life.