Notable tidal wells and springs in Wales include:

St John's, or Sandford's Well Porthcawl (GB Grid: Map 170 837774)(*p.132).
Chepstow Wells, Chepstow - two wells near Bridge St. (*p.196). These are probably the wells mentioned by Bradney*: see Note on Wonder 6
Carncwn Well, at the foot of Carn Ingli, on the Newport to Cilgwyn road, (*p.212).
Ffynnon Lygaid, South side of Castell Clegyr Boia, St David's, Pembrookshire. (*p.213).

Of course, it is quite possible one or more of these have nothing to do with the tide. Ebb-and-flow wells and springs are frequently called "tidal" when they just have a cycle which is twice daily. Gerald of Wales implies this of two in Wales (*p.139;196) and one in Ireland (*p.62 - probably the famous Corann well*). Infact, the name "Tidewell" was applied more generally to ebb-and-flow wells whether they were synchronised with the sea tides or not: for example, the well known "Tideswell in the Peak District fluctuated four times an hour. While the hydrology of such "reciprocating" or "intermittent" springs can be extremely complex, the classic explanation through syphoning is described under Wonder 6.

Other ebb-and-flow wells/springs in Wales include:

St Non's Well near St David's (GB Grid 751243; 40m OD) (*p.210).
An Anonymous 1823 poem "The Marvels of Wales" apparently mentions an ebb and flow well near Rhuddlan(*p.82).
Llandyfeisant Well(?) Carmarthen. (*p.171)
Ffynnon Leinw, Cilcain, Flintshire (*p.180).
Maen Y Milgi, Llandrillo(*p.193).
Ffynnon Olden, 500 yds NW of Little Newcastle (*p.213).
Pencw Wells, Pencw headland above Goodwick, Pembrookshire (*p.216).