Do not buy a power bank only by the mAh number printed on it. Some of that capacity is lost during charging, so the real charge you get is lower than the printed figure.
Things to understand:
1. A 10,000 mAh power bank usually cannot fully charge a phone as many times as the number suggests. The real count depends on your phone battery.
2. Check the output watts. If your phone supports fast charging, the power bank should support that speed too.
3. Ports: having both USB-C and USB-A is convenient.
4. Safety: look for protection against overheating and short circuit, and a trusted brand. A mark like BIS approval is good to see.
5. Weight: a large capacity power bank is heavy. If you carry it daily, take a smaller one.
6. Air travel: a power bank usually has to go in cabin baggage. Check the airline rules beforehand.