Kinter is trying to sell a small 2 x 8.5W amplifier marked 500W. I have recently opened one of these amplifiers and I found a SANYO LA4508 integrated power amp inside.
This amplifier is actually specified for 24VDC and gives only around 2 x 3W at 12V.
After what I can see there are other brands with similar products looking almost alike the "Kinter 500W". I doubt that there is any big differance inside.