Hi,
I am looking at following :
[...]
Basically, they're all the same voltage and current, but the last one has got more specs (if they hold, it sounds really good, perhaps too good) even if in a semi-funny machine translation. Don't let the "free gift" of one lousy alligator clip lure you into buying #1, they're dirt cheap.
Apart from that, calculate the true price (i.e. including shipping to your home address) and pick the cheapest - not much difference anyway.
I have read that desirables are : needs to have a +ve and -ve voltage apart from the ground, it needs to have a range starting from zero. Any others? Any views on these options listed above?
Not sure if that's what you mean, but none of the supplies have a negative output. They have 0V, +V and an earth connection (connected to the housing if metal, that you'll only have a use for if your mains supply connector carries a ground pin (not all do) and even then, I wouldn't let that be a deal breaker - a 4mm socket in the rear, wired to the metal housing (or the transformers iron core) , is both cheap and easy to install.
People claiming that starting from 0V is important is usually the type that think that we should all be driving a Lamborghini, even when shopping groceries.
Lab supplies either start from 0V or from 1.25-1.50V.
Most amateurs (and a good number of pros) will never need less than 1.5V (and the unlikely event a diode or two in series with the output will get it down).
What's important is that the current limiter goes down to a very small current, preferably a real CC mode. Some high current supplies are lousy in setting low currents, like eg. 2mA in a 5A unit.
Most people will be just as well off with a stepped voltage control. Some people just goes overboard on the dial, insisting that 12V is 12.00V (= pure insanity) - [12V 1% means a range of 11.88V to 12.12V and most people will do excellent with a tolerance of 5%] and that worry is removed with a stepped control.
From that philosophy, I built a supply for my brother. It has got steps for 1.5V, 3V, 4.5V, 6V, 9V, 12V, 15V and 18V and he's never needed anything besides those values (during ~15 years) and no voltmeter is needed.
Stability (step response and load-/line regulation) is an extremely important parameter (or rather a set of parameters), but most first time buyers neglect this, of ignorance or because the numbers aren't always available.
Anybody serious about electronics should have (at least) 2 lab supplies:
One for high currents which can have a stepped voltage selector (or not) and a lower current unit eg. 1A max. with a continuously variable and easily settable current limiter and here the voltage should be continuously variable and going from 0V will help if/when using it for reference voltages (if it is stable enough).
The latter is an obvious choice for DIY, but large current supplies have become so cheap, that you cannot get the parts and box alone at a competitive price (unless you're able to design and build a switch mode PSU).