Electronic warfare is a 'black art' even amongst the west, and very little about it is made public.
The PLA seems to be giving EW extremely high priority, as I cannot remember the last time the PLA conducted any sort of drill or exercise where strong EW interference was not simulated.
The PLA has put a great deal of effort and resources into their EW. They would have definitely benefited from having access to the Russian EW gear supplied with their various Flanker purchases, and it was likely that the Israelis might have pass along some tips before the Americans put their foot down the the Falcon deal, and maybe even afterwards for all we know.
And lets not forget that PLA scientists must have had a field day when that EP3 came down in Hainan. I know it's not a dedicated jammer, but the two are close enough that access to that airplane is likely to have greatly benefitted China's EW efforts.
The PLA now have dedicated jammer versions of the Y8, and we have seen pictures of JH7s testing out what could only be a comprehensive tactical jamming pod suit similar to what the Growlers are sporting.
But the main thing is, that is about all we can tell from appearances, but it's what is under the hood that makes all the difference, and we are not likely to know that for another few decades, if ever.
I also find the prowler story very dubious and hard to believe. Did anyone live near Nanjing during this incident? If there really was aggressive jamming by prowlers powerful enough to cripple the military grade communications of the entire Nanjing MR, what must it have done to the civilian stuff?
I also think that the Vietnamese Su30 story, even if true, would not be the most objective evaluation of the PLA's EW capabilities.
The Vietnamese bought pretty much the same Flankers as the PLAAF. That meant that the PLAAF would have had extensive experience and knowledge of both how the Vietnamese Flankers EW suit worked, but also figured out how to counter it with their own EW exercises.
It is similar to how the Israelis were able to so effectively jam the Arab SAMs after they had time to get a few examples and study them; why the US and western powers are so keen on getting their mitts on the latest Soviet/Russian systems, and also why China is so keen on replacing the equipment on their J11s and Russian supplied Su27s with home grown equipment.
However, since the PLA is almost certain to not have actual examples current US or western frontline jamming kit, I dare say they will not be able to do so well trying to jam US or western types.
But the thing is, Chinese avionics and radars are advancing so rapidly, and are indigenously developed, so the western powers probably have very little idea of what the PLA is capable of either. Thus it is pretty much impossible to predict how a EW showdown would end between the PLAAF and a western power, so the issue is usually ignored. Not the most logical or realistic thing to do, but its the best we can manage with what little we know.