Is it possible to blow out a candle flame using pure oxygen?
It depends on the wick.   A flammable wick, exposed to oxygen, will burn, but
a non-flammable wick, saturated with liquid wax, could be chilled by the gas flow,
and when the evaporated wax is blown clear of the wick, the candle flame
could extinguish for lack of fuel.   Basically, the oxygen flow might
(at sufficiently high velocity) remove the vapor fuel so that the flame
becomes a detached fireball, and the wick and wax of the candle cool.
The oxygen flow just has to be faster than the flame propogation in the
fuel-oxygen mixture.

A solid flammable wick, though, won't be displaced, just burn faster,
and on discontinuing the oxygen, the candle will still be lit.