Try one and see what happens.
Chinese wall-warts and power supplies, especially ‘bargain’ ones are notoriously noisy in the RF department. Get an SDR, plug in a chinese power adapter and observe bands of noise from DC to cosmic rays.
Bkmk
My understanding is the same as what you were speculating on - that it is a controlled charge. In the old days, the adapter just pumped power into the batteries, whether they needed charging or not. “Modern” adapters when paired with the matching battery bank will attempt to optimize the charge to what the battery needs to maintain a charge, provide a full-charge, or just maximize battery life.
It’s logical then to assume that you need to match the power-adapter you purchase to the device you’re charging, following the manufacturer’s specifications.
Most if not all “brick” power supplies and any power supply inside a standard desktop computer is a “switching” power supplies. They develop their output by rectifying and filtering a high-frequency (maybe 100 KHz) oscillator inside. One of the several advantages of these types of power supplies is that they do not need a heavy-with-iron power transformer. If you have some device that uses a “wall wart” type of external supply, maybe 2” x 2” x 2”, you may note that such a supply is fairly heavy. That’s because it has an iron transformer inside. Those are called “linear” supplies. Should you wish to develop 6.7 amps out of a linear supply, you’d probably be looking at a fairly heavy item. Switchers are more efficient; but they tend to fail a bit more and they almost inevitably place residual noise (from the internal oscillator) on the DC power they are designed to create. In most cases, that noise does not matter, or, stated differently, the thing the power supply is designed to power up is immune from such noise by design.
Without going into further minutiae, you have the right idea. Switchers almost universally require a load to work. Linears do not. They do their voodoo without any load placed across the output. If you go to youtube and search for “PC desktop bench supply” you find multiple videos where folks converted a PC power supply into an experimenter benchtop supply. Which is pretty cool, because presumably you can get an old PC power supply for free from a discarded computer....unless the supply itself is the cause of death. You might have to pay $100 for a benchtop experimenter power supply....but of course, you don’t have the meters, the pretty case, the carry handle, the convenient binding posts. But that’s “experimenter” tradition. My point is, that EVERY one of those projects requires placing a load resistor across the output wires of the adapted PC power supply. The load resistor fools the switching power supply into thinking that the device it is supposed to power is actually there when it isn’t.
You might have to introduce a small load (resistor) across the output to get the PS to fire up. Then you can measure actual voltage.
Yeah, the charger detects if the battery is low so it can stop charging when it is no longer needed. That’s why some chargers have a light on them, so you can see (if it is lit) that it is still charging, and if the light is off, the battery is fully charged.
I assume you are aware that on Dell chargers the center pin is NOT part of the power supply output but some sort of sense line so the laptop knows how many watts the power supply is?
Look closely at the plug and you’ll see that the outer barrel is double-sided, with metal contacts on both sides—that’s where the output of the power supply is connected.
Some pictures here show exactly what I just described:
A good test if the adapter is charging is to have it plugged into the wall outlet then using your tongue, touch the tip of the other end....