Depends when your other SD3 came into existence.
Between circa March with the introduction of the Alu Bed to around Sep, it would seem that the heated beds shipped such that they had 80°C limits. At one stage, SolidoodleSupport confirmed that this was their limitation.
At some point following their switch to the printrboard clone, the beds changed again, and went back to supporting up to 110°C. This change they haven't exactly owned up to or spoken about - its anecdotal based on what people are seeing with 'new new' SD3's (able to get to 110°C) and that their Printrboard Firmware changed the bed MaxTemp back to 150°C up from the 'older' 110°C
All of this is to say - yes, there is SD3 beds in circulation that only get to around 80-85, by design.
Now - regarding the difference of Benchsupply vs The SD supply - not knowing what bench supply or specs it has, its hard to say specifically, but, lots of bench supplies are going to be capable <12Amps of the SD supply, and many supplies are also limited in their ability to output current at lower voltages (My daily user does this - its a nice PSU, just gets ripple to hell and back at high current low voltage..) meaning that the fact it only got to 60° may not be unsurprising - Ultimately its Current that dictates the heating rate, not so much the voltage (meaning, you can run 12V, 1Amp and take 2 hours to reach 80, or you can run 9V 9A and take 10 minutes to reach 80....).
All you can do is confirm with SolidoodleSupport that you have one of the 80°C limited beds... and then decide.. do you pay for an overpriced fractional step up, or just go and buy a PCB MkII or QU-BD bed and sort it once and for all for the same price ....
Regardless, rest assured, theres little point in 'pulling the bed apart'... You either have an 'in spec but underpowered' bed, or, its faulty, in which case, you need to just replace the whole silicon pad as a whole (or switch to PCB MkIIB, etc).
