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Yes, it's ALWAYS the slave, the gadget, that decides what charging current to take, even on USB C.
A USB "A type" host port or charger signals usually with fixed voltages or resistors on the data lines of USB what current can be supplied.
The standards are only universal for 100mA (original USB 1) and 500mA. Apple may use a different standard for 1A and higher.
If the gadget doesn't understand the "signals" (they are not actually serial data), it may assume 500mA, or even 100mA.
The 5.2V is likely an absolute maximum and usually there is little or no difference between 4.8V and 5.2V.
If the Host voltage is too low the gadget stops charging. If it's too high it's destroyed.
The USB C hosts/chargers have two distinct modes: (1) The output is 4.8V to 5.2V and it works like a USB A port. (2) The output can be a much higher voltage so that say 2A is very much more power, more like a laptop charger (which are 14V to 20V depending on models). I don't remember what the maximum voltage is.
100mA gadget: Any charger/host port
500mA gadget: Any USB 2.0 host port or 500 mAcharger. Some USB 1.1 Host ports.
1000mA (1A), 1500mA (1.5A), 2A etc: The charger that is recommended or came with the gadget as not everyone uses the same scheme. Otherwise charging is only at 100mA or 500mA
Some laptops with USB 2.0 or USB 3.0 Type A host ports can supply more than 500mA, but the gadget only takes more than 500mA if the scheme is compatible. So a 1A Apple thing (maybe a USB DVD drive) will work on a same generation Mac and most later ones, but may not work on ANYTHING else, even a powered USB hub, because it can't "see" the condition on the USB D- and D+ pins that mean 1A or more available for a USB gadget.
Some "Battery" power packs are rubbish. The weight can be guide. Some use the older laptop type metal cased round Lithium cells and some use the flat bagged Lithium cells (Li Poly). A few mad ones use disposable cells!
I've a pocket one with a solar panel which would need desert sunlight to charge it even in a day. It might take many days outdoors here and won't charge with normal indoor lighting. A solar panel able to charge a gadget in real time would be quite large!
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