We have and use the GPP-4323 and SDP3303X-E (have 3). All have the ability to be placed in Series or Parallel mode without any additional external cables/wires, so perform just like a single PS with additional Voltage (60V) or Current (6A). Both have USB and LAN, the GPP also has RS232 interface, and the GPP has 4 independent programmable channels, SPD has 2 independent programmable, and one fixed (2.5, 3.3, 5) channel.
The GPP has a unique built-in load capability on 2 channels, the SDP can be user calibrated (the GPP can't) and can be user "enhanced" to an SDP3303X (1mv and 1ma resolution), the GPP has 0.1mv and 0.1ma resolution.
The SDP UI is a little more quirky than the GPP but both require a little getting used to. The display screens are the same size, however the GPP screen can be setup in various ways (5 settings), very nice feature!
These are what one might consider "Lab Quality" Power Supplies, stable accurate voltage and current settings, low noise, no voltage overshoot, fully programmable, quality build and low fan noise. BTW both types have shown very low drift & noise (GPP < +-1mv long term drift with <80uv SD, SDP <+- 2mv long term drift, <40uv SD @ 10V).
The GPP costs ~$760, the SPD ~$400.
Best,