Does Popular Science's GAOFEN 4, The world's most powerful GEO spy satellite, continues China's great leap forward into space label as most powerful GEO spy satellite refer to optical resolution, electrical power, or ability to knock out satellites on the other side of the GEO orbit with laser beams? That last one is meant in jest.
If it is optical, and the resolution at Earth's surface is 50 meters (as mentioned in the article) at 36000 km that's 1.6E-06 rad. With a wavelength of 500 nm $\displaystyle 1.22 \frac{\lambda}{\theta}$ suggests an aperture of 40 cm.
That's about the same size as the cameras on deep space or planetary science missions, LEO spy satellites have apertures of 1 or 2 meters (or even more perhaps). Here's what a 1.5 meter spysat looks like. Even Hubble in LEO is 2.4 meters and if it were just a 21st century technology telescope and imager with a lighter mirror and none of the other science packages, I think it could have been lofted to GEO.
Is it really a roughly 40 cm camera (16 inches) that is making Gaofen-4 the most powerful GEO spy satellite? It certainly looks like a 40cm telescope in this photo:
above: from Spaceflight 101's Gaofen-4 Earth-Watching Satellite put into on-target Orbit by Long March Rocket. Photo credit: CAST via Xinhua
Gaofen-2 employs CS-L3000A bus, configured with one 1 meter panchromatic/4m multi-spectral camera, with designed lifespan of over 5 years. (my emphasis)
The payload fairing is 4.2 meters in diameter. If Gaofen-4's multispectral camera is using a 4 meter aperture, that sounds powerful to me, but I'm not sure why it would be limited to 50 meter resolution on Earth. And if 40cm is in fact the most powerful camera in GEO, I'll also be surprised.
edit: the answer was clear, I just needed reminding that this part was about Gaofen-2 and not Gaofen-4.