All you need is a multitester or multimeter....to check the polarity on ur Adopter (positive and negative).Yes you can use external power supply to power up phone for unlocking.Check fones battery which points r postive and negative.But there is one thing u must remember....the adopters which doest have regulated out put...can seriously damage the fone.
If ur doing V3x...there is an easy way to do after connecting TP...you can put the board in the back cover only to hold the battery.A little of common sense is needed always.
