I just thought this might be a good reasonably current place to share my USB serial mod of the RS-232 adapter. I just used a bog standard USB - serial interface board from ebay, but I think the tweaks to the meter end might be an improvement on some others I've seen. As far as I can remember, it just uses the original parts for the receiver section (eg. Moving Q2 onto the Q3 footprint). I did add a 'TX' LED, in the provided PCB mounting hole (and drilling out the case hole), driven by DTR. This works with a corresponding phototransistor inside the meter, driving the serial data enable pin ('RS232') on the ES51922 chip (trck cut required), so that the meter will perform a normal sleep power down if the logging software isn't running or the adaptor removed.
Unfortunately I didn't document the PCB track cuts (and some of them are not visible, but it ought to be reasonably easy to reverse engineer it from the schematic and bare PCB image.
Sorry that it's badly documented, but maybe of help to somebody. I've attached modified interface schematic (the original is included in a corner of the UT61E meter schematic available on the web), bare PCB image (found on the web), my modified interface board, and the completed adaptor, (with USB-serial interface shrink sleeved).
EDIT: Original RS232 Interface schematic added for reference. +/-12V supplies derived from by DTR and RTS.