Today is the start of April. Official News has it that tariff will be increase with immediate effect.

For Detail News, Click Here (PDF).
ELECTRICITY TARIFF REVISION FOR THE PERIOD 1 APRIL TO 30 JUNE 2012

1. For the period from 1 Apr to 30 Jun 2012 the electricity tariffs will increase by
4.3% as higher fuel prices have resulted in higher power generation costs. The average
fuel oil price over the last three months (1 Jan to 15 Mar 2012) increased by 7.3% from
S$127.07 to S$136.37 per barrel. This increase in fuel oil prices saw a corresponding
increase in the price of natural gas which is used for power generation in Singapore.

2. The electricity tariff for households will increase by 4.3% (or 1.19 cents per kWh)
from 27.59 to 28.78 cents per kWh. This will increase the average monthly electricity bill
for families living in four-room HDB flats by $4.18.

3. SP Services reviews the electricity tariffs quarterly based on guidelines set by the
Energy Market Authority (EMA), the electricity industry regulator. The latest tariffs given
in Appendix 1 have been approved by the EMA.

_______________________________________________________________________________________________________

Issued by: SP Services Limited
10 Pasir Panjang Road #03-01
Mapletree Business City
Singapore 117438
Co. Reg No : 199504470N
www.spservices.com.sg
_______________________________________________________________________________________________________

So with that said, It's about an increment of nearly $3.01 during peak hour (aka 7am - 11pm) $1.71 for off peak hours (11pm - 7am). Refer to the PDF Chart via the above link for more insight.

You can use the Electric usage calculator from AQ to further compute your cost.

Further Reference Point:
AsiaOne News released yesterday.