With the soon to be expected mass production and commissioning of KJ-500s, I think the PLA in a few years will have one of the largest fleets of heavy/medium weight AEWC in the world.
PLAAF and PLANAF together have 4 KJ-2000s, and about 12 KJ-200s, for a total of about 16 heavy/medium sized AEWCs.
Russia at latest estimate has 16 A-50s of various variants in service, with many to be replaced by the new A-100s.
US currently has 32 E-3s for USAF and 62 legacy E-2s with new E-2Ds to be built.
Other countries have smaller numbers of AEWC, such as Japan with 4 E-767s and 13 E-2Cs, or Pakistan with 4 Erieyes and 4 ZDK-03s, or Britain with 7 E-3s, Australia with 6 E-737s... etc.
If KJ-500s are built in similar number to KJ-200s (and I think there is a good chance they will, given PLA's insatiable need for better command/control and redundancy), I think the PLA could very well end up with about 30 combined KJ-2000s/200s/500s in total, which would be quite a formidable AEWC fleet, and could quite conceivably vie for second place behind the US in terms of number if not capability.