Rpi3B+ from AliExpress OK?
Yes, should be OK, except perhaps a little bit more expensive.
A couple of years ago, an old version of Rpi was manufactured in ShenZhen, China. And the PCB colour is red (China Red!). Now all Rpi's are manufactured in Sony Wales, UK, so I have heard.
These years I used to buy Rpi's from RS and E14 Hong Kong, shipped from UK via Singapore, and found no problem. Last year I bought a couple of RpiZs and RpiZWs from one of the authorized Rpi resellers in China. It is a TaoBao (AliExpress) shop in Shanghai. Again I found no problem, same price (converted to RMB), same versions of Rpi.
I bought the Rpi's from an authorized TaoBao/AliExpress reseller in China, and not from other non-authorized shops, because those fake shops often buy the goods from UK or US, or from eBay (when everybody can buy one only), say, and then resell it, marking up price 30% or more, so it is not worth it, except to those rich guys with too much money to spend. I think it is legal, except there might be a warranty problem
I think it is very very unlikely that there is another Made in China version of Rpi.
BTW, Rpi3B+ out of stock may be a good news, implying that Rp4 is coming to town! :)
Differences between Raspberry Pi B, B+, A+, 2B, 3B - Jarvan, Elecrow 2017dec21