Hi I've adapted the code from the old 1.x version of PasswordMeter for Ext 4. It is based on the code posted by yyjia on his blog. I've adapted his code to use the fieldSubTpl instead of adding elements after render time. Also I align the meter to the inputfield (I prefer it that way )

password-strength.png

Code:
Ext.define('Ext.ux.form.PasswordMeter', {
    extend : 'Ext.form.field.Text',
    alias : 'widget.ux.passwordmeter',
    inputType : 'password',

    reset : function() {
        this.callParent();
        this.updateMeter(this);
    },

    fieldSubTpl : [ 
        '<div><input id="{id}" type="{type}" ', 
        '<tpl if="name">name="{name}" </tpl>', 
        '<tpl if="size">size="{size}" </tpl>',
        '<tpl if="tabIdx">tabIndex="{tabIdx}" </tpl>', 
        'class="{fieldCls} {typeCls}" autocomplete="off" /></div>', 
        '<div class="strengthmeter">',
        '<div class="scorebar">&nbsp;</div>', 
        '</div>', {
            compiled : true,
            disableFormats : true
        } ],

    // private
    onChange : function(newValue, oldValue) {
        this.updateMeter(newValue);
    },
    /**
     * Sets the width of the meter, based on the score
     * 
     * @param {Object}
     *            e Private function
     */
    updateMeter : function(val) {
        var me = this, maxWidth, score, scoreWidth, objMeter = me.el.down('.strengthmeter'), scoreBar = me.el.down('.scorebar');

        maxWidth = objMeter.getWidth();
        score = me.calcStrength(val);
        scoreWidth = maxWidth - (maxWidth / 100) * score;
        scoreBar.setWidth(scoreWidth, true);
    },

    /**
     * Calculates the strength of a password
     * 
     * @param {Object}
     *            p The password that needs to be calculated
     * @return {int} intScore The strength score of the password
     */
    calcStrength : function(p) {
        var intScore = 0;

        // PASSWORD LENGTH
        intScore += p.length;

        if (p.length > 0 && p.length <= 4) { // length 4 or
            // less
            intScore += p.length;
        } else if (p.length >= 5 && p.length <= 7) {
            // length between 5 and 7
            intScore += 6;
        } else if (p.length >= 8 && p.length <= 15) {
            // length between 8 and 15
            intScore += 12;
        } else if (p.length >= 16) { // length 16 or more
            intScore += 18;
        }

        // LETTERS (Not exactly implemented as dictacted above
        // because of my limited understanding of Regex)
        if (p.match(/[a-z]/)) {
            // [verified] at least one lower case letter
            intScore += 1;
        }
        if (p.match(/[A-Z]/)) { // [verified] at least one upper
            // case letter
            intScore += 5;
        }
        // NUMBERS
        if (p.match(/\d/)) { // [verified] at least one
            // number
            intScore += 5;
        }
         if (p.match(/(?:.*?\d){3}/)) {
            // [verified] at least three numbers
            intScore += 5;
        }
 
        // SPECIAL CHAR
        if (p.match(/[\!,@,#,$,%,\^,&,\*,\?,_,~]/)) {
            // [verified] at least one special character
            intScore += 5;
        }
        // [verified] at least two special characters
        if (p.match(/(?:.*?[\!,@,#,$,%,\^,&,\*,\?,_,~]){2}/)) {
            intScore += 5;
        }

        // COMBOS
        if (p.match(/(?=.*[a-z])(?=.*[A-Z])/)) {
            // [verified] both upper and lower case
            intScore += 2;
        }
        if (p.match(/(?=.*\d)(?=.*[a-z])(?=.*[A-Z])/)) {
            // [verified] both letters and numbers
            intScore += 2;
        }
        // [verified] letters, numbers, and special characters
        if (p.match(/(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[\!,@,#,$,%,\^,&,\*,\?,_,~])/)) {
            intScore += 2;
        }

        var nRound = Math.round(intScore * 2);

        if (nRound > 100) {
            nRound = 100;
        }
         return nRound;
    }
});
And for the CSS:
Code:
.strengthmeter {
    background-image: url(../images/meter.gif);
    background-size: 100%;
    width : 100%;
    float: right;
}
 
.scorebar {
    background-color : white;
    float: right;
    line-height : 6px;
    width : 100%;
}
You can find the background image here.