I think this is him him in 1901:
41 Bethesda Street, Merthyr
RG13/5031/94/24
Joseph Power, 52, underground labourer, b. Dublin
Mary A, w, 51
Ellen, d 25
Edward, s, 19, ripper in colliery
Mary, d, 16
Joseph,grdsn, 5
Edward, grdsn, 1
Al but Joseph snr were b. Merthyr
I can't find Joseph James in the baptisms but this looks like his birth registration:
Joseph James Power, Oct q, 1895, Merthyr Tydfil, vol 11a, page 654
If you could order this, it should give his parents.
Gadget