Here is my comming of using powerpoint to a group of audience (regardless of size, 2-2000+). PowerPoint is not ideal to present complicated, detailed tables/charts. All charts and tables should be concise and "not busy" to the eyes. I found that any charts with more than 4-5 lines and audience would lose attention/focus/interest. The same can be said of bar charts. If you have a bar chart without a dominating bar or one that can stand out, it is very difficult to convey your story.
Back to your original question. I create excel charts within Powerpoint. Once complete, I just manually position the chart to a predetermined position and sizes (if I'm presenting many charts of the same size). That way, the charts don't look to be bouncing around when you move from one slide to another.
Like oldchippy said, it is better you set up your own style. If the charts come from others, good luck reformating them. That's why I would try my best getting the direct data (or re-create the data if it is stated) and make my own charts. So all the charts would look consistent in style, color theme, size and position.