Despite the Jonsbo claiming it supports mATX, that's not strictly true as it only has two expansion slots, same as most ITX cases.
If you are getting a Pentium in the G3420 range, I'd suggest looking at the G3258 as it's not a lot more expensive, slightly faster and is quite unique in that it is overclockable. You'd need a Z-series motherboard to actually exploit this feature, which is out of your price range, but if you came to upgrade your CPU somewhere down the line, I'd be willing to bet the 3258 will hold it's value a lot better than it's brethren and you might be able to recoup a lot of what you spent.
I'd be very wary of any "no name" PSUs. AcBel are an OEM supplier for a number of brands, but only on very low quality. These days it's super easy to make a PSU conform to 80Plus Bronze standards, and while it's not a measure of the quality of components, any PSU that does not have this is likely pretty poorly made, not to mention the fact that despite being named a "400" it can only supply 300W at the very most.