Actually, that power meter is nowhere near similar to the one you want to build. It only measures DC, not AC and tHe electronics inside run off of 5V and it is powered off 60VDC. 60VDC which is an conversion ratio of 12:1 which is near the maximum that you can have in a single DC-DC power supply stage. If you go very far beyond that, you start needing multiple stages in the power supply (which means you need multiple power supplies cascaded with each other). Practical power supplies DO have a limited input voltage range that depends on the output voltage you want.
You never specified if the line voltage was DC or AC. Finding high DC voltages is rare (like 1000V) because it's so complicated to build DC-DC converters. You *might* find that voltage in things that might use giant DC motors electric cars or trains. But everywhere else, you're much much more liklely to run into AC voltages that high because it's much easier to get an AC voltage that high and bring it back down again using transformers (which you can't use with DC). So you can just use transformers then to bring the AC voltage down to an AC voltage just a bit higher than 5Vrms and then use a regular AC-DC converter to turn that low AC voltage in 5VDC. But you still need multiple transformers with handling a small range of input voltage.
If you design one product for different input voltage ranges, you are basically designing multiple products but putting them into one box. Just build one for the regular 120VAC or 240VAC line voltage (and maybe add in a separate power supply input to run off DC voltage as well so your circuit can be line powered with DC voltages and then also design your measuring system to work with DC as well as AC). Then you can also power the circuit off of the line voltage MUCH more easily. 120VAC, 240VAC and <48V are the voltages you can actually find to test. Think about it, if you did build a 600V AC or 600VDC circuit, how would you ever find that voltage to test it? How would you ever find 5kV to test it? Would you ask for permission to hook your circuit up to some electric train tracks? or a power substation? or a manufacturing plant? Probably not. Could you even get parts that were rated for 5kV? Or build a PCB that can handle 5kV? Probably not.
Of course, if you only care about AC, then you don't need to make your measuring system capable of handling DC as well and you don't need to have a separate line powered DC power supply option. The difficulty is how to make a high voltage AC measurable by electronis running off low voltage DC. So there are two problems to deal with:
high voltage AC vs low voltage DC
You can use transformers for this or you might use a resistive divider. Either method will produce a lower AC voltage signal.
bipolar AC vs unipolar DC
Obviously DC electronics can't directly measure an AC voltage signal when it goes negative (and might be damaged by it). There are also a couple ways to deal with this. YOu might rectify the signal or you might bias the signal. Or you might have electronics that run off of a +/- voltage.
There ICs out there that are made to measure energy and power. They have fast, accurate ADCs that sample voltage and current at high speeds. THey also do things like integration and calculation of the measurements they take to give power, energy, and phase. Each of these ICs also uses one of the methods above to solve those problems- but you still need to add some external components that won't fit inside the IC (like transformers, high voltage resistors or rectifiers). You just need to add the external components in the same way the datasheet tells you. Here are two examples.
https://www.analog.com/en/analog-to...rgy-measurement/ade7768/products/product.html
**broken link removed**
You'll notice that
Just making a 120-240VAC power meter (whether or not it is lined powered or battery powered) will keep you busy for a while.