BK Precision 1550
This is a switching supply.
The up-down adjustments would make this a non-starter for me.
CSI3005X5
A whole bunch of companies re-brand this unit. They're actually fairly decent. The voltage pot is a 10 turn, the current limit is button-driven in 0.03A increments.
The most common resaler of the power-supply is MPJA. It also comes in a bunch of voltage and current ranges: 0-30V 5A, 0-60V 3A, 0-120V 1A.
One thing you can't see in the pictures is that the unit has a set of screw terminals in parallel with the output banana jacks, below the cover plate labeled "EXT OUTPUT". If you need more permanent connections, you can use the screw terminals.
The schematic for the whole supply is available. This makes it enormously more repairable (and hackable) then ANY of the others.
BK Precision 1671A
The funky extra output connections on this make me nervous (speaker terminals? really?).
I would guess that the potentiometers are single-turn, both from the artwork on the case near the knobs, and the fact that it does not mention multi-turn knobs, as that's normally a significant selling point at this price range.
On the whole, If I had to choose from the supplies listed, I would wholeheartedly recommend the CSI3005X5, more because the alternatives are considerably worse.
Anyways, I would say that even if you don't think you need a floating output power supply (what you really mean when you discuss a separate earth terminal), you almost certainly will find it useful in the future, so I think you shouldn't dismiss it. Just being able to string multiple power supplies in series for higher output voltages is tremendously useful.
This type of power supply only has one regulator placing a settable voltage between the + and - (red and black) terminals.
The green terminal ties into the safety GND of the power cord and hopefully to the earth grounded network in your building.
In operation of the power supply you have the choice of a fully isolated output or you can tie one or the other of the + or - terminals to the green terminal if you want to have the supply output referenced to the safety ground.
Best Answer
Because that covers the operating voltages of the majority of electronics circuits for auto, audio, computing and industrial applications.
Correct, in general, but the current limit has many useful applications:
Forget about electrons in wires. It will lead you into all sorts of confusion. Just think of voltages, currents, power and energy.
There is a component - a very low resistance - maybe 0.01 Ω, for example. If the voltage were to stay at 18 V then a current \$ I = \frac {V}{R} = \frac {18}{0.01} = 1800\ \text A \$ would flow. The power supply can't deliver that so the current limit cuts in and the voltage collapses to the voltage drop across the component at the current limit. In this example, on a 3 A supply, that would be \$ V = IR = 3 \times 0.01 = 0.03 \ \text V \$.
Figure 1. A typical bench PSU.
Depending on the PSU's voltmeter resolution the display may give an all-zeros reading for a short-circuit test.