They did beef up the power supply a few years ago, when new facilities on the up side at the western end of the Bourne Valley viaduct near Branksome, were constructed.
x2 Cl.442 did and x2 Cl.444 and Cl.450s do run into the carriage sdgs west of Poole where, as a previous post had said, any uncoupling takes place. I don't ever recall seeing them in multiple beyond that point though.