High powered is the phrase that sells the worst telescopes on the market, because power sounds like capability and means magnification, which is set by a twenty dollar eyepiece rather than by the instrument in front of it.
What power actually refers to
Magnification, which is the telescope's focal length divided by the eyepiece's. Change the eyepiece and the power changes. Any telescope can be made to give any magnification on paper, which is why the figure appears on the boxes of the least capable instruments and almost never on the boxes of the best ones.
The ceiling that no eyepiece raises
A telescope can only separate detail down to a limit set by its aperture, and past that magnification enlarges blur. The working rule is about two times the aperture in millimetres, so 150x on a 76mm instrument and 260x on a 130mm. The atmosphere usually intervenes below even that, which is why 150x is the practical ceiling on many nights.
The most powerful telescope you can actually buy
Read as aperture rather than magnification, that is a large dobsonian: amateur instruments of half a metre and beyond exist and are sold, at prices and sizes that make them a project rather than a purchase. Read as magnification, the question has no answer, because the eyepiece decides and the air disagrees.
What to buy instead of power
Aperture, then a mount that holds still, then good eyepieces. Those three in that order decide everything a telescope can show, and none of them appears on the boxes that lead with a magnification figure.
Questions people ask about telescope
What is the most powerful telescope you can buy?
Measured properly, the largest aperture: amateur dobsonians beyond half a metre exist. Measured as magnification, the question is meaningless because the eyepiece sets it.
Is high magnification good in a telescope?
Only up to about two times the aperture in millimetres, and usually less because of the atmosphere. Beyond that the image is larger and worse.
Why do cheap telescopes advertise huge magnifications?
Because magnification costs nothing to claim and depends on the eyepiece rather than the instrument. It is a reliable warning sign.