From Tekkenpedia

Supercharger, as its name goes by in Tekken Tag Tournament's command list, is a common move for every playable character in all Post-Tekken 2-games, excluding Tekken 4. It brings the character into a state of what is known as Ki Power, hence the more popular name Ki Charge.

It is executed by pressing down all attack-buttons (Left Punch, Right Punch, Left Kick, Right Kick, also written as 1+2+3+4) simultaneously. The fighter will then glow with his or hers standard charge glow for 55 frames (0.91 seconds) during which no other input can be made. After the charge-up is completed, the fighter's hands (when standing still) or attacking limb will glow with light blue energy for 120 frames (2 seconds). This time frame ends prematurely if either side connects an attack.

There exist alternative ways for characters to achieve a state similar to Ki Power, without using the super charger, such as Paul Phoenix being in full crouch for 1½ second (only applies to T4 and above), Doctor Bosconovitch pressing 3+4 when standing, etc. Please refer to each characters respective movelists or the respective moves for more information.

[edit] Advantages/Disadvantages

Ki Power gives the character the following advantages while in effect:

• The character will inflict 1.4-1.5 times more damage than normally on his/hers fist attack (does not apply to throws)
• The first attack will have Counter Attack properties
• If the attack is blocked, the opponent receives 10% of the normal attack damage as guard damage

Ki Power gives the character the following disadvantages while in effect:

• The character will be unable to block
• The opponent will inflict 1.4-1.5 times more damage than normally on his/hers fist attack
• The first attack of the opponent will have Counter Attack properties