Tom, sorry to be so long in replying but I've been working out a lineage from Burke's and trying to mesh it with my own data. Trying to trace the Powell's from America to Wales is difficult at best so I decided to try to reconstruct the Castle Madoc lineage. I have been unable to find anyone so far who claims lineage from the Powell's of Castle Madoc who has validation of that lineage. So I have used "Burke's A Genealogical and Heraldic History of the commoners of Great Britain and Ireland Enjoying Territorial Possessions of High Official Rank: But Uninvested With Heritable Honours." It is available on Ancestry.com. The info comes from Price of Castle Madoc. The Price's inherited Castle Madoc title from the Powells in 1798 when the last Powell died with no heirs carrying the name.
The Burke's account is the most substantial information that I have been able to locate but it does not give many solid dates. I would welcome information from anyone who is working on this line of Powells. If you are interested in what I have so far, I would be happy to email it.