The Breviate Chronicle for the year 1042 notes:

bellum pulld?wach in quo hoelus victor fuit Grifinus captus est a gentilibus dulin (Gough-Cooper, b1063.1).
Translation: the battle of Pwlldyfach in which Hywel was victorious. Guffydd was captured by the heathens from Dublin (Remfry, 173).

The Brutiau narrows down the location adding `And there Hywel defeated the Gentiles who were ravaging Dyfed? (Jones, 25).

Pwlldyfach has plausibly been associated with a place name near Cynwel Elfed (SN 373 277) in Carmarthenshire (Lloyd, 360). No further information is known (Charles-Edwards, 562).

RCAHMW (Battlefields Inventory), Dec 2016

Bibliography
Charles-Edwards, T. M., Wales and the Britons 350?1064 (Oxford University Press, 2013).
Gough-Cooper, Henry (ed.) The Breviate Chronicle: Annales Cambriae, The B Text from London, National Archives, MS E164/1, pp. 2?26, online edition.
Jones, Thomas (ed. and trans), Brut y Tywysogyon or the Chronicle of the Princes: Red Book of Hergest Version (Cardiff, University of Wales Press, 1955).
Lloyd, J. E,, A History of Wales from the Earliest Times to the Edwardian Conquest, third edition (Longmans, Green, London, 1939).
Remfry, Paul M. Annales Cambriae: A Translation of Harleian 3859: PRO E. 164/1: Cottonian Domitian, A1: Exeter Cathedral Library MS.3514 and MS Exchequer DB Neath, PRO E. 164/1 (Castle Studies Research, 2007).