I bought an AR and OT as soon as the black OTs were available to pre-order at Andertons (in the UK). The AR came with a PSU-3b, and when the OT arrived a couple of weeks later, it came with a 3c. However, the OT developed a fault with one of the LEDs, so I asked for a replacement. The 2nd one came with a 3b. I thought it was odd at the time.
The 3c’s do seem “nicer” in the way you describe. I think I prefer that my two Elektron PSUs match, now, tho’. Before I kept thinking about which one to plug into which device (I unplug them most days because I shuffle my desk a lot).