Can anyone identify these PCB connectors?
OK, so I've figured this out, though I've thoroughly confused myself with the vagaries of TE connectivity part numbers.
#1 and #3 are both TE Connectivity Power Double Lock Connectors.
#1 is the 3.96 mm pitch, 3 position

Header: 179839-x
Plug: 177899-x
Locking plate: 177919 (optional, fits in back of the plug to keep the contacts more secure)

#3 is the 6.5 mm pitch, 3 position

Header: (1-)179846-x
Plug: 179938-x
Locking plate: 316062-1

Both use the same contacts:

Contact 26 - 22 AWG: 179592-1 or 179592-2
Contact 20 - 16 AWG: 179593-1 or 179593-2
These are the part numbers for loose contacts, they're also available in strips.

#2 is also from TE, but the Power Key 5.0 series

Header: x-1376383-x
Plug: x-1376389-x
Contact 24-20 AWG: 1376348-1 (only available in a strip)
Contact 20-16 AWG: 1376347-1 (only available in a strip)
Locking Plate: 1376395-1