Bad capacitors. It's always bad capacitors (and it's never Lupus).
They've dried out and become resistive. In the process they sometimes make life ugly for power transistors and diodes.
If you're not safe with some mains voltage (there may be some in the hot side of the supply) please don't open the box.
Look for swollen electrolytic capacitors (metal cans). Replace with reputable parts with same values (no consumer components supplier will sell parts as nasty as a cheap manufacturer can buy wholesale).
Check diodes and transistors on output side for blowage.
Main high voltage mains side capacitor might be dried out. Shows up as overload in feedback paths and shutdown. Replace it. Must be same voltage rating!
Go see the sci.electronics.repair FAQ.
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.
Best Answer
No, you can't generally parallel multiple supplies and get higher voltage. Each supply will regulate to a specific voltage. Even if all are rated the same, some will be a little higher and some a little lower. The ones set a little higher will take most of the load. There may also be oscillations as the multiple supplies try to fight each other. In no case does this have anything to do with making more voltage.
It is possible to parallel some supplies to achieve higher overall current. However, the supplies need to be designed or rated for this. Switchers are often easier to design for paralleling. Some even have a current sharing signal. This signal is connected between the supplies, which is used to level the amount of current each supply produces. Some supplies achieve this instead by having a somewhat soft current limit. Even if one supply is set a little higher than the others, it will hit its current limit and its output voltage will drop a little. This causes other supplies to kick in and start producing current to hold up the bus. This is generally not considered as good as deliberate current sharing, but it can work with the right design.
In any case, you're going to need switchers one way or the other. You want 1.4 kW out, so dealing with waste heat is going to be a major design issue. Even at 90% efficiency you still have 156 W of heat to deal with. That's not trivial. You say switchers are too costly, but what you want to do is not trivial and doing it right will cost. If you think switchers are too expensive, take a look at the total cost of the alternatives!