Wifi adaptors using RTL8188CUS driver will not work in ad hoc mode. If you plan to use your raspberry pi in ad hoc mode, you must verify that your adapter is using the nl80211 driver.

In general, devices with RTL8188CUS work great as wifi access point.

You may need to enable the non-free repository in your package manager's settings.

If you need to install a driver yourself, chances are that it is in your distro's non-free package repository.

Therefore, you may need to plug the Wi-Fi adapter into a powered USB hub.

A Wi-Fi adapter will probably need more power than the Raspberry Pi USB port can provide, especially if there is a large distance from the Wi-Fi adapter to the Wi-Fi Access Point, or it is transferring large amounts of data.

Raspberry Pi 3 Model B has a BCM43143 on board.

World's easiest way to setup the WiFi AP - tested with Lightberry Wifi (RT5370 chipset).

Installing the TL-WN722N adapter - also for other adapters under Debian Squeeze.

Hotspot - WiFi Access Point - tested with a TP-LINK WN725N (RTL8188CUS chipset).

CLI configuration instructions - tested with an Airlink 101 AWLL5099.

Many of these are applicable to many adapters.

Setting tl wn727n to modem