The best replacement for plug in is add on.

The best alternatives to plug in are rated as following:
★★★★★  add on
★★★★  volt
★★★  hybrid
★★★  chevy volt
★★★  hardwired
★★  prius
★  reed diffuser
★  nissan leaf
★  applet
★  hard wired
★  plugin
★  hardwire
★  prius hybrid
★  active x
★  air wick
  electric vehicle
  prius c
  chevrolet volt
  google earth

Your alternative for plug in is not listed? Suggest!
Speaking about plug in, one probably shouldn't forget about winamp.

Other search terms related to plug in and their ratings are:
★★★★★ winamp
You have in mind a companion for plug in and it is not yet here? Propose!



Google Trends

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plug in
add on
volt