This put me onto the possibility of fakes https://www.microchip.com/forums/m1016224.aspx
The ones I had showed the same issues with the date code looking wrong, should start with the last digit of the year then a 2 digit week number. Fake example in pic.
Bought some more from a local electronics supplier and presto, is capable of delivering 250mA and esp is working perfectly with no large scale caps. (with wifi connected its drawing about 80mA)
I suppose my lesson is always to test components in isolation first including to the performance specs you need. Plus of course being aware of possible quality problems with ebay china components.