There are typically 3 things when connecting a device to power:
1. wall outlet
2. extension cord/phone charger
3. device being charged or powered
Each has watts/volts/amps labeled. With W/V/A, how do I determine if a system is safe or unsafe?
In: Physics
Safe for your person? Then unless they look completely broken, burnt etc most consumer devices are generally safe to use if there is no abuse. (ie don’t stick a screwdriver in a power outlet etc). It isn’t recommended that you open things up and try your hand at rewiring things unless you know what you’re doing.
Safe in the sense that it won’t damage equipment. First, know your region’s standard power – there are (very broadly) two standards for consumer power outlets ~100V and ~240V. There is also multiphase power but you should probably not encounter them too much (and they come with a different looking plug)
Second, look at the device that plugs directly into the outlet. There should be a label and there should be something that looks like “INPUT” or “Input voltage”. If this matches your region’s power, then the device can be plugged in and be expected to work with no damage. Most phone, tablet and computer chargers are universal – expect to see “INPUT 100V~240V” or similar. These can be plugged into any consumer outlet without issue.
Extension cords are convenience devices – they don’t change the power and voltages. The general rule is that if the plug fits the outlet, it is probably safe to use (check for wiring damage if you are concerned) It is recommended that you use these extensions for mostly low powered items and never plug one extension cord into another. Things that are generally “high powered” – electric kettles, microwave ovens, ovens, electric heaters, electric cookers, refrigerators, room heaters (see the trend!) These devices should have their own dedicated plugs, if possible, or not used simultaneously for long periods if sharing an outlet (this is ultra safe).
Power is generally not an issue (see above). Devices draw as much power as they need and won’t “overdraw” power. The higher power the device, then it will require more current (power = current x voltage). An outlet with a limit of 13 A (common in many places) can provide power for a total of ~1500 W (in 110V regions) or around ~3000W in 240V regions. If you don’t stack extension cords or plug in multiple high power devices, this is very much more than needed for things like device chargers which are usually < 100W or perhaps a large laptop possibly 150W or so.
There is a lot more nuance to this but it is not necessary if you’re not going to poke inside the electrical wiring.
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