Advantest R6161
This is the most precise (6.5 digit) and accurate (30 ppm in 180 days) voltage and current source Advantest makes. ADCMT has a newer version (6166) with identical specs and a new processor board.

It is a little below a Data Precision 8200 in terms of accuracy, but with more ranges and much higher power.

My unit does not have the 100 mA option for the 1000 V range and is limited to 12 mA there. It was received red tagged "after multiple attempts unable to repair" but was tested and works fine.

Perhaps what is most interesting is the voltage reference inside is an unheated zener diode. (the Data Precision 8200 uses an LM299) It is trimmed to 10V with an LT1001, a custom resistor network, and a series of jumpers. The output is determined with PWM, but this has not been investigated yet.

It also has a voltage divider on the front end that can be enabled to produce 1000 mV, 100 mV and 10 mV ranges, albiet with much worse output impedance.

That's all I can think of for now.

All photos taken by myself (safedork). I prefer to licence under CC-BY-4.0 https://creativecommons.org/licenses/by/4.0/
Let me know if this is an issue.