When you begin talking about telescopic distances, you need to consider not only the strength of the telescope, but also the size of what you are trying to see. A cheap telescope would have no trouble seeing an elephant a mile away, but might have difficulty with a mouse.
When it comes to astronomical distances, it depends on what kind of telescope. The Hubble Space Telescope can see several billion light years. However, it is seeing light that left its source several billion years ago, not what is happening right now.
The simple answer: about 3/4 of the way across the Universe.